First off, you need to have the paid version. The free version sadly does not seem to have pregnancy for anyone else
The ones I managed off the top of my head was (SPOILERS INCOMING)
All four sisters
Susan (The mother)
Adriana (the secretary at Discreet)
Riley
Megan (Bella's friend)
Ana (James' sister)
Alina (Ana and Rachels friend)
Kira (Ana and James' cousin (I think?))
Iris (the wife of the priest guy)
Rebeca (artist lady on the island)
Nia (artist lady's daughter)
Miley, Sabina and Sasha (the three women from the flashback stories)
I thiiiink those are all... I may have forgotten some.
Except for the sisters and the mother, all pregnancies happen in the epilogue sadly.
To make it happen, I mainly just picked the creampie option whenever possible. If you want to know the specific choices to get all those in your harem at once, then I followed a guide (mainly this one: https://steamah.com/sisterly-lust-full-walkthrough-all-30-days/ )