To either date em or to get to have sex with her all the time
Anna, Dora, Mako and Rebeca you can have sex all the time dependant on choices at the start and how fixated you were on your creampie routine.
Maria you can in the office but there is a specific day that she will get pregnant, i don't remember if its a random day or not.
Vicky you can fuck at the start and you can have one child with her.
Ema you can trick her the first time to have your child without her knowing and later on at a club date with James(couldn't get her pregnant there even with ovulation day).
Alina and Zara you can bang at work in the massage room after a few conversations and dates.
Teodora is very easy to start her romance and when you do you can bang her until she becomes pregnant, after that you can't anymore(at least not in this version).
Julia you have to keep meeting her at your weekend jobs and later at the gym until you are banging her at her home, after that if she becomes pregnant its again another one locked out of sex until later version of the game.
Paola you meet at some point in your new home and if you keep visiting her you will eventually go through some events that will lead to you being able to have sex with her at the end of your mid day visits.
Naomi is completely dependable on Moko.
Elena you can fuck until she gets pregnant(havent played enough to know if she becomes available after a time when she conceives).