I don't know if this would work but maybe a message from the girls or a dream showing like the MC spending time with, for example, Alex and the baby as a "family outing" would be interesting. I don't see a way the born baby could be involved in a loop in the game without feeling weird or making weirdos jumping to inappropriate conclusions. Just want to see the MC be a good dad. And for fun at the end of it, they put the baby in the crib and head to Alex's room to work on the next baby. This scenario could be applied to Carla, Haily, or Lina if it fits with them better than Alex.
Seeing Carla's twins in a mail would also be special, that was a awesome surprise. Also, the Friday dinner comment of "working fertility advertisement" that Lin says was very funny given the situation. Bonus points for comedy Nunu. I love this game so much. It has been my stress reliever for over a year. Also, a random question, what made you choose to give Carla twins? I love it.