Also, remember that the Dev has been very specific on letting you choose if you creampie or not, so Preg isn't a for sure outcome or even the canon ending.
People we can probably rule out are:
Rachel (currently)
Bella
Mom (she does sex work for a living, I think she's smarter than this)
Adrianna (same)
Ana and Alina (pretty much sluts at the beginning of the game, they're already on the pill most likely)
The two from the island. They have sex with their brother/son on the regular.
Likely:
Iris (Get pregnant to escape her loveless marriage)
Liza (Because she would love the idea of carrying a baby, especially one given to her by her loving brother)
Miley (Because the MC was an idiot during that sex scene)
3rd place:
Riley because "Ooops?"