well after doing some love/lust stat tinkering on the calendar with Christine on the Corporate route, i put her love higher than her lust 2 choices before making the choice of getting her pregnant. raised her love a few dialogues before the "do it" #378 on the walkthrough, the choice before the "fuck her" choice in where she gets pregnant. she stayed at the end. if you sleep with Jessica on the couch in the cabin, you have the 2 girls for yourself to keep as Christine is fine with you doing Jessica. even end up doing 3-ways routinely apparently. sadly, you don't keep Sonya. she quits and finds herself another man in this route. so i guess you can have a max of 2 girls for an ending. too bad you don't get further content with Veruca after she gets pregnant, she doesn't even bother to tell you.