Short Version:
Maybe P is overwhelmed by bookkeeping and it's distracting him from situational awareness. Help him make a mechanically very simple character without fiddly bits or conditionals to keep track of, so he can focus on making good choices rather than having good bookkeeping. Invite the other players to support P with advice and by being good role models for the behaviour he's trying to cultivate.
Long form answer, with rambling and details.
Back in my very first RPG ever--and also my first time as a GM--I had a player whose poor choices got him repeatedly killed. Let's call him Q.
Q knew the rules and mechanics quite well, but had a very hard time applying them intelligently to whatever situation he found himself in (like forgetting to heal himself as a cleric). Even more than that, though, was his role-playing: he really really liked to role-play his characters, but that got him in trouble because when Q got deep into his character's internal motives the PC would lose common sense and perspective about the surrounding context of his actions.
It got bad. Really bad. Q's second character was killed by the party for betraying them (he had a conversation about his friends over tea with a "nice" lady). At that point I shared Making the Tough Decisions with the group. He studied it carefully, had intense discussions with me about it... and as a direct result his fourth character perished of untempered curiosity: the characterisation "very curious" overcame the common sense "half these items are cursed and my friends are begging me to stop," until the pile of treasure he was investigating yielded up a lethal curse.
After that session I took Q aside and we talked. He knew he had a problem, and he was trying to "get better," but he needed help. I'd noticed that all his PCs so far were mechanically complicated and required in-game bookkeeping: advanced casters and races with lots of conditional features and spell-like abilities to keep track of. So we hatched the simplest possible character build: nothing to keep track of. No "if you're flanking, X also happens," no spells, no per-day abilities. If his character sheet said he could do a thing, he could always do it.
We wound up with a kind of Indiana Jones flavoured skillmonkey (a rogue chassis with homebrew mods to replace things like sneak attack because tracking whether you can deal that extra damage was beyond what we wanted for the build). He wasn't optimised in the traditional sense--but since another PC in the party had straight levels in the NPC Expert class, that wasn't an issue in keeping him relevant in the group. Instead he was optimised for what Q needed: a simple no-bookkeeping character to let him focus on situational awareness and making good choices.
At the end of each session he'd hang back --along with any other players who wanted to-- and we'd reflect on the game: what worked, what didn't. We'd consult (and if necessary research) and come up with what to make sure we did again, and what we'd change next time. (I've since found that any game I run which has some form of this "reflect and plan" dynamic after every session is improved by it.)
In tandem with another player rising to the challenge and being a kind of "teach by example" role model, it worked. A year later Q was successfully running complicated wizard builds with great party dynamics and great depth of character. He was a real joy to work with, and all he needed was to wade in at the shallow end of the bookkeeping pool instead of jumping into the deepest part head-first.
nota bene: My players have tended to treat the group dynamic as one of table-level cooperation between friends. However much their characters may be rivals, at the table they collaborate to tell the best stories, and I'm also one of the collaborators. In groups where players and/or the GM act as rivals at the table level of things, I'm not sure how much my experience will be useful. It sounds like your whole group isn't really on the same page in terms of their desired gameplay experience, and communication isn't really strong. Working on improving the "friends at the table" level of things might help your game in a number of ways.
To my mind, the overriding rules here are these:
Alternate Form
The creature retains the type and subtype of its original form.
Undead Type
You cannot have an undead that has a Constitution score, so since Alternate Form has you retain your type, you cannot gain a Constitution score. I believe this is “more specific” than the general rule that you gain the target creature’s physical ability scores when using Alternate Form.
You could argue the opposite way, however, that Alternate Form is a more specific case than the general rule that undead do not have a Constitution score. But note that this results in a living (has a Constitution score) undead (retains that type), which to me is a good enough reason to side the other way.
As for using Charisma in place of Constitution, this is a common feature for undead, but not a universal one. In some places, that privilege requires a feat (e.g. Undead Meldshaping in Magic of Incarnum). Depending on your build, I might want to tax you for it; Cha-to-everything is a fairly potent strategy as it is, and undead is a desirable type anyway. Getting to use Charisma for yet more things, and avoiding the “weakness” of the undead type’s lack of Constitution, might be problematic. But if you weren’t already pursuing a Cha-to-everything build, I’d probably give it freely.
Best Answer
I’d say those guides are wrong.
Racial bonuses don’t tend to be super-important in general; as long as you don’t literally have a penalty to an important score, it’s probably fine enough. What are some things a druid wants from his race?
A bonus feat. Well, yes, dwarves don’t get this and it’s amazing. Shame to miss out. But this also applies to almost-everything that isn’t human. Even beyond that, druids need exactly one feat: Natural Spell. After that, everything else is gravy, and unlike literally every other class in the game, it is optimal (barring planar shepherd, which you should) to take 20 levels of druid without multiclassing or taking a prestige class, so druids don’t have to burn feats on meeting prerequisites.
A bonus to Wisdom. Dwarves lack this, but it’s also extremely rare in the first place. The only options are decidedly weird, not to mention frequently banned: anthropomorphic bat (blatantly overpowered), buomman (can’t speak), jermalaine (Tiny-sized and ridiculous ability scores), and lesser aasimar (clearly overpowered, though not as much as anthrobat).
A bonus to Constitution. Hey, dwarves have got this!
Some way to communicate while in Wild Shape. Options here are rather limited, but a few races exist that do it.
So yeah, humans are probably better druids than dwarves. Which is nearly meaningless, as humans are probably better than almost anything else at almost everything. For the dwarves, the Constitution bonus is good and the Charisma penalty is minor. The bonuses on bull rush, trip, and various saving throws are quite nice as extras. The weapon familiarity goes to waste, and the armored movement thing is a bit harder to use, but those are minor anyway. The low land speed doesn’t matter much because it’ll be replaced when in Wild Shape.