That word applies to one of them more than the other one. She needs more time and other events to develop.
After Debbie's stunt (and Kate saying the doors open inwards) it won't work

. But it won't be needed. Kim wants to have that conversation, she is only waiting for the right moment.
The problem with spreading the pregnancies in time is that it would require a lot of work (and in-game time). Imagine Eileen for example; you can get her pregnant in 0.4, 0.7, 0.15, or a later date before the trip to Aruba. I literally can't afford to render her in 4 belly development states (plus one non-pregnant state). Last time I animated her it took more than 2 hours to animate her hair only (per animation), plus the posing, and rendering time (the last animations I bought and used with Norah and Samantha are 400-450 frames long and would take ~10 hours per animation to render with Eileen's hair). If I should multiply all of those times by 5 instead of by 2 (pregnant/non-pregnant) the after-Aruba updates will take 4-6 months to do.
I understand why most games avoid pregnant sex (especially if pregnancy is optional). It's a lot of work. The poses and animations should be adjusted a lot and the pregnancy assets aren't too good. You also have the issue of which poses work well with pregnant women (no more missionary, for example), so you are limiting the choice of poses. That's one reason to have (at least) seven unpregnant women in the third act (6 new students + Meemaw). I can still use those poses that won't work with pregnant women.
The synchronized periods will be alluded to after the Aruba trip (they will have lived together, or almost, for more than six months) depending on the pregnancy status.
My Plump Princess sounds fine. It will be used but not overused. Referencing her (perceived) body size would mean other girls could react to it.