Presuming, assuming and all that, is quite fine. It is really.
What you kinda missed, is that the game isn't even at half time. How do I know that? Well, having sex with Nana (Allison) is more or less the middle of the game.
There wasn't, so far, any talk about any time-skip. So, you'll have a full harem of pregnant girls (of many ages). About your worry about the girls being past the menopause, well, in this alternate universe where the game happens, the MC's supersperm, solves that issue. EVERY girl in the Harem (take note, IN the Harem) will be pregnant, or not, your choice. Except the 7 main ones, those are not subjected to choices.
Why did I mention the Harem? Because there are several LI's that will not be in the Harem. It is unclear if some of them will still be able to be impregnated.
About the pregnant tag, well, it will be the player's choice if they get pregnant or not, again, exception made to the 7.
The babies, well, Tanya's baby is about to be born (if you allowed it), she'll be the oldest. Next will be Paveena's (if you chose that). Then...... the full kindergartens... or only the 7's babies.
So, for all the points of your post, you don't need to worry if you made the right choices, or you can replay and do them now.
BTW, instead of presuming ill intentions and writing in an accusatory way, you could have simply asked.
Peace