Regarding the concerns about pregnancy content getting overcomplicated over time, I've never been a fan of having it be the very last thing that happens in a game.
Maybe it would be worthwhile to set up something basic - a chat option for the girls to come off BC, pregnancy/breeding kink variant dialogue during PIV or when you let the girls pick where you cum, a random chance for pregnancy rolled at the end of sex, then a one-time dialogue when she informs you. Questions about timeline/alternate art/forking the story don't come up until you let the pregnancy progress, so you could just leave it there while you hammer out the details.