More the stages development. Something where the pregnancy progresses over time. Not one for preggo sex myself but sure add that too. This should also affect the dialogues the MC has with the pregnant party/parties and the dialogues the NPC's have with each other.
EG:
(1)You could sleep next to 18 and she wakes up because of morning sickness, feeling the baby kick etc.
(2)You could enter the hallway and 18 could be talking to Heles about a potential sibling, or talking to Bulma about how she's gotten swollen feet or much hungrier since the conception etc.
(3) There could also be quests/side quests tied into it. Such as the pregnant party sending you somewhere to acquire more comfortable clothes, a birth pod (whatever the saiyan babies go into after birth), construction of a nursery at the palace
(4)21 could also have experiments in her lab where you impregnate followers/people that pray to you in the universes to kinda build up some sort of elite guard, soldiers or whatever to do your bidding across the universes you control or to be used as future NPC's for plot purposes.
In terms of development the hyperbolic time chamber could come into play where we could skip the total 9 months or see the progress over 3/4 weeks from a small baby bump to a full out big ass womb.
In terms of the children you the creators can decide whether they'd be part of the main plot or not but the hyperbolic time chamber could also come into use here too(training them for your own purposes etc) and a slower progression system could also be used such as 8/10 weeks from infancy to adulthood due to 21's food supplements or whatever
Just spit balling off the top of my head!
Hope it helps
Masq
EDIT
You did really well with addressing fan's concerns/wants with the game in the latest update. That was well done!