My game will likely figure a mix of some of these (maybe not so much the romance option).I think you have a couple of options to prevent a total breakdown.
One of the players in particular - and the one whose PC is the most obvious source of disruption (a chaos sorcerer with Demonskin Adept PP and Primordial Adept theme) - has already taken proactive steps to try to make cosmologically-driven links, both in character and in setting up backstory, that can help unify the party. The PC is also a Corellon cultist, and a Chan (good archomental) cultist, and has built up backstory about the relationship between Chan and Corellon, and between Corellon and the Raven Queen. And two PCs are Raven Queen cultists (one a demigod cleric, one a paladin Marshall of Letherna).
Oddly enough, the one who may in fact being most disruptive (though not looking it on the surface) is the almost utterly unbending invoker (Divine Philosopher, Sage of Ages) servant of Erathis, Ious, Bane, Levistus (the trapped archdevil), the Raven Queen and (sometimes) Vecna, who is trying to reconsruct the Sceptre of Law (= Rod of 7 Parts, or 5 parts so far) and destroy all remaining primordials.
It will be interesting to see how it unfolds.