Vance was very much an asshole when he appeared (and later disappeared) in the game a few years back. Vance, then, had maliciously planned ahead and separated Ethan from Nat so he could try to get his clutches on her for his self-centered interests. We all know this, and we kinda suspected this character to return (due to character assets and sprites that not all characters at the time had, and the dev being noncomital to writing him off completely). And now to refer to an old post of mine on a fun,
non-serious speculation...
But
what if...
"...the couple learn that Vance is actually a truly an upstanding guy with a tortured past and take steps to help him under their nurturing wing?" Y'know to heal his wounded heart <3 , à la Carl-esque style, and to teach him to become a better man and grow as a person and step away from his past dark life with a full redemption arc. Ethan and Nat comes to care for him while Vance have a good,
wholesome relationship with them, and looks up to Ethan as sort of a "big brother" figure and wants to emulate him so that he could live a more righteous life (and perhaps would do anything to protect the couple from other bad actors that's already in the game). Wouldn't that be an intersting twist by subverting many possible expectations folks had for Vance, the guy with a tortured past looking to redeem himself but never knowing how to go about it?
Don't take this post seriously -- just having fun and poking holes in things.

Cheers and have fun y'all!