Scrying allows you to see a place somewhere else:
You can see and hear a particular creature you choose that is on the same plane of existence as you. (…) Instead of targeting a creature, you can choose a location you have seen before as the target of this spell. (…) the spell creates an invisible sensor within 10 feet of the target. You can see and hear through the sensor as if you were there.
Teleport says:
This spell instantly transports you and up to eight willing creatures of your choice that you can see within range, or a single object that you can see within range, to a destination you select. (…) The destination you choose must be known to you, and it must be on the same plane of existence as you.
How difficult it is to teleport there depends on your familiarity with the location. If you are "very familiar" with the location, then you have a 75% chance to land exactly there, and only a 5% chance for a damaging mishap. Very familiar is described as
"Very familiar" is a place you have been very often, a place you have carefully studied, or a place you can see when you cast the spell.
Assuming you are scrying on a location, can you then teleport there as if you were very familiar with the place?
(I am asking as I am not sure if you can see the other willing creatures, and at the same time see the place through scrying. The question is not about if the caster could spend a lot of time studying the place with scrying and become very familiar with it that way).
Best Answer
This is exactly how we rule it
On multiple occasions our party has done the remote view/teleport routine.
Unfortunately, that doesn't get you better than "very familiar", so there's still a 24% chance of things not going as planned.
Even worse, the DM rolls, so things that might affect a die roll don't apply.
Assuming you're not engaging in some clever shenanigans, the caster has to be casting scrying (or clairvoyance or similar), and so there's an added slot cost.
There really isn't too much room for debate as to whether this works
At least by RAW, at least with scrying.
A minimally cooperative DM can quibble with you. They can state that the seeing in the teleport spell requires direct vision with the eyes. I think that's a dubious ruling, but they're the DM, it's their game.
The spell literally gives scrying as an option in describing false destinations:
Furthermore, the scrying spell in particular does not say that you're blind to your own senses while scrying. You don't even have to use an action to scry, once the spell is successful, so the ways the spells are written, you should be able to cast scrying, get a lock on your target, then cast teleport.
Whether the scrying/teleport combination works has never been a subject of debate at our table. We don't have a perfect record of arriving successfully though....
Other methods of remote sight
Other methods of remote sight need to be addressed individually. Key points are:
Does it blind you to your own senses, if so it's hard to argue that you can see the destination and the creatures to be teleported at the same time
Does it take an action to do the seeing, if so, it will be challenging to see and teleport at the same time.
In either case, you can work with the DM to whether it is sufficient to see the teleport destination and THEN look at the creatures to teleport, or vice versa; that is not really that much of a stretch.
In addition, you can work with the DM to determine what constitutes "carefully studied", since that also counts as "very familiar", then you do longer need to see it while teleporting.
PS
We had a discussion on this particular combination of scrying and teleporting, and whether you automatically get surprise, just from teleporting. We agreed to a table rule that merely teleporting will not grant surprise, so that neither the PCs nor the monsters can get surprise just from teleporting.