Short Answer: You can consider the adventures mostly ordered in terms of difficulty as well as character level, but not all of them are "the deadliest in history".
Tales from the Yawning Portal is an excellent book; a collection of some of the great adventures in the history of Dungeons and Dragons. You're looking at a source for seven adventures, all varying in difficulty and length. The promotional description may be a little generalized though. The better description is A collection of exciting and challenging adventures that gives DMs resources for one off adventures for all player levels. Sure, Tome of Horrors are only for DMs looking to eliminate player characters, but the others run differently, and each are challenging in their own way.
The Sunless Citadel and The Forge of Fury are the lowest level, and (relatively) easiest adventures of the book. Citadel is a great one off specifically for 1st level characters. The Forge is perfect as an immediate run right after The Sunless Citadel. These are perfect for teaching new players or those with difficulty with traps on how to handle themselves properly in dungeon crawling. Deadly rating: Not so much. Average difficulty.
The Hidden Shrine of Tamoachan is the next adventure in character level, but definitely takes a climb up in difficulty. Traps are devious. The treasure inside is a little sparse, and may not be worth the danger inside. Even if the players survive the adventure, there is a chance that the dungeon can trap them in, and force them to be new slaves for Tamoachan! Deadly rating: Deadly. Beware.
White Plume Mountain mellows out the challenge a bit, taking an expected challenge for its level range. If the party keeps a level head, the incredibly creative puzzles and environment encounters are not too overwhelming. They are definitely creative, and usually do not take a linear approach like standard traps. So if your players are not used to handling that, it will be difficult! Deadly rating: kinda deadly.
Dead in Thay is really a series of adventures in a super dungeon, and expect this one to compete with Against The Giants for the longest. This one is a collection of very creative "rooms" that all rolled up into a marathon of encounters that will drain your players of their spells and powers per day. Resource Management will be the silent killer in this one. Pay attention to the risk of character death in this place, because if certain conditions are not met, any resurrected character will find their souls trapped forever! Deadly rating: Deadly
Against the Giants is another one that really is multiple adventures. It is three different modules, that will send the players on a tour of the different types of Giants. All of the Giants are dangerous in their own way, so if the players do not adapt their tactics and evaluate their enemies, then they could find themselves in trouble against one type or another. The difficulty evens out for this one though, as it offers some separation between modules, which means a change to rest and recharge - something not readily offered in Dead in Thay Deadly rating: Not so much, Average.
Tomb of Horrors ... Evil. Just ruthless and pure hate. Run this if you promised your players that you would kill some of them. If your players have any trouble with handling traps or figuring out puzzles, it's all but guaranteed to be deadly. There's false entrances that may even be trapped that prevent the party from even entering! Inside, there's a seemingly innocent trap that levitates a player... into a chamber where their only real options are to starve or die of thirst, or run into another room to be assuredly chopped to bits. Then, there is another trap with a chance of being magically stripped of all of your possessions, and then teleported out of the dungeon entirely. Those are just two of the thirty-something encounters of this dungeon. 'Nuff said. Deadly rating: Over 9000. Side effects include: possible rash, intense weeping, may ruin friendships.
Talk to the players.
The party isn't doing anything wrong per se. Proper use of choke-points is in fact good tactics, especially if they don't have a strong need to move in and surround the enemy. (If the party had a bunch of melee guys getting screwed over by the tactic, then it would stink.)
But the easiest thing might be to talk to the players. Acknowledge that they've done nothing actually wrong but bring up the points you have brought up here, that it's just not very much fun for you, and maybe for them.
Refuse to engage.
To quote the usual message: "If the party can do it, so can your monsters."
The players like to huddle up in a corridor and refuse to come out? Why would the monsters stand there in the open and try to break through instead of retreating and waiting for the PCs to move?
Encounters as laid out in the book are only the general suggestion of how something works, but unless your monsters are mindless or of merely animal intellect, they should be able to easily recognize the strategy and move to the sides, out of the line of fire of the "nukers" in back. Stalemates aren't fun, especially if there's also some incorporeals or patrolling monster squads hassling the back line (though that depends on the specific fight at hand). Keep in mind that fights are loud, and big evocations doubly so; you have every justification you need to bring random wandering patrols down on the party's back. Just be careful that this strategy makes sense in context; if the party gets jumped by patrols when they fight in hallways but doesn't when they go into the room, it's gonna feel unfair (because it is) and set up a players-versus-DM mentality that you really don't want to encourage in a game.
But, back to the point, the monsters could definitely retreat under fire and pull back into their own hallway position, or even leave the area entirely. Too often I see PCs playing with smart tactics while the monsters just growl and run at the party over and over. Only mindless creatures would do that; an obviously overmatched party of intelligent monsters should retreat, regroup, reinforce.
Engage on their own terms.
On the same basic level as above: Anything they can do, you can do. ("Better" is a matter of debate.)
There are very few monsters who totally lack ranged options. If the party likes to huddle in the back and lob spells, arrows, and cantrips, the monsters can absolutely respond in kind. Orcs can throw spears and axes just as well as they can charge in swinging. If the party insists on standing in a tightly clustered hallway position, use their tactic against them. Fireball and lightning bolt can be highly effective against a group that insists on standing in a straight line.
An extended artillery battle might not be much fun, but if they're gonna play games with doorways, you can play right back, and suddenly moving in close to prevent such a standoff seems a lot better.
By the way, keep in mind that you can take an action at any point during a move, so it's completely valid to have a lich standing to one side of the door, out of easy line-of-sight, then run into view, fire a spell off, and move back into cover on the other side of the doorway. They can ready attacks to hit him when he appears, but it's not a foolproof plan since there's also spells like invisibility and mirror image out there.
Enforce the rules
It's entirely likely that any direct attack made while trying to "shoot over your party's shoulders" in a cramped hallway would invoke a cover penalty on the guys in back. Based on the Dungeon Master's Guide rules about cover when using miniatures (DMG p.251, with diagrams on 250), it's hard to imagine any arrangement of characters as described that wouldn't have 3/4 cover against virtually any target they want to shoot at. They might be able to arrange to have merely half cover against some targets, depending on how you read the cover rules, but in general, firing between allies would be a lot like shooting through an arrow-slit, so 3/4 cover sounds right.
However, ranged attacks from the monsters would have the same penalty against the back-liners, so this isn't actually a solution as much as a way to make the party have less fun and even more dependent on area effects (where cover is measured from the origin point of the blast). Everyone getting a +5 to AC will make fights stretch on and on, and makes it feel bad to the players to keep rolling misses.
Spread out the monsters.
Both tactically and strategically. If the party is relying on throwing area effects, make sure you keep your monsters spread out so only a few can be affected at a time, and maybe break up a big fight into a few smaller fights where they'll have to blow through more spell slots if they want to keep doing their shtick. And along that line...
Don't let the party rest easy.
This strategy seems to me to be very spell-slot-intensive. They have to keep the front line healed, and get almost all their damage from big damage spells like fireball. That suggests to me that the party may be sleeping more than normal, and that you might be allowing them to go take a long rest any time they want to.
Pressure the party to hurry up with time sensitive missions. Launch ambushes if they sleep in the dungeon. If they leave the dungeon to rest, the monsters use that time to reinforce their numbers, reinhabit rooms previously cleared, set guards or traps, block doors or build barricades, summon demonic defenders, and so on. Make the monsters at least as tactically smart as the PCs are. Let the party know that relying almost entirely on the spellcasters' damage output is not going to cut it.
The module is only a suggestion.
The module should not be treated as a bible. Encounters can and should move around, DMs are encouraged to add or remove creatures to make the fights harder or easier, and so on. Tune your adventure to the party, if necessary. Don't feel constrained by the words on the page.
If they're depending heavily on spells for damage, counter magic with magic when you can, especially if they keep leaving the dungeon to "wait until tomorrow". The local spellcasters can and should adapt to their strategies by preparing protection from elements, wall spells, even globe of invulnerability if the levels are high enough. Keep in mind that a simple fog cloud can be utterly devastating to any ranged combat tactics, and a wall of fire blocks line of sight in addition to pulsing fire damage onto the party and forcing them to either back off or run through. Old standbys like grease and web are some additional fantastic low level options for making an area very undesirable to the party; personally I love web because of the irony of punishing the players for failing to move around by making it impossible to move around.
Best Answer
The books are designed to let the DM choose how to connect them. There is no 'you must play XYZ book before ZYX book' ordering, except insofar as levels restrict. (It would make no sense to finish Rise of Tiamat then jump into Curse of Strahd, for example, since COS ends at a lower level).
While SKT is written with the assumption that HotDQ/RoT has already occurred, there are even notes inside it on how to invert that paradigm if desired.