Having all of the girls from the previous games would be a monumental task, so I wouldn't get your hopes up on that. Breedtown 4's cast is going to be mainly made up of characters from past games, though! (At least, that's what I heard from the Patreon. I don't know if anything's changed on that front.)
As for Incest, I'd say there's not a chance there. Not only has Brandon himself said that he's not a fan of it, but there's no way he'd be capable of encountering a relative in 4 (that he's be willing to fuck). At most, we might breed a sister pair or mother daughter pair in 4, but that's dubious at best.