iserith
Magic Wordsmith
They are mature players and I think they can handle this.
If you only think they can handle it and do not know for certain, then it sounds like you haven't had a conversation about this sort of thing with the players prior to kicking off the campaign.
And if you haven't, you're well-advised to do so before any player takes unilateral action against another player's character.
In my campaign, if any player attempts to attack or otherwise hinder another player's character, the player of the character who is being attacked or hindered gets to decide how it is resolved. This generally has the effect of stopping any sort of thoughts of PVP in its tracks, but leaves the door open to players mutually agree to such conflict, if it helps the group achieve the goals of play, that is, everyone having a good time and creating an exciting, memorable story in the doing.
So, again, if you haven't discussed with the group before, now's the time, even if it potentially ruins the surprise. Better that surprise is ruined than the entire play experience in my view, especially right at the end of the adventure path. It's best to go out strong than to end on a sour note.