When you are roommate with Lily, Jill or Lisa you can watch TV with them in the evenings. Start off slow and watch romantic movies with them.
When you stop getting points with them change to watching porn and start touching them later on.
When they are in the bath room try to go in and if they don't kick you out, you can try bedtime activities with them. This is generally how you get new scenes with them.
Lily: you need o take her out on a few date and show up for work when she is working at the store. After you've finished work you go home together and you get a sex scene before going to the diner for dinner. After a few dates try and have sex with her without using a condom.
Change to Jill as a roommate and continue having sex with her until Lily catch you in the act a few time, she will eventually stay and watch you have sex with Jill and will join in later.
To get foursome with Jill, Lily and Lisa:
You must have had sex with all 3 of them without using a condom.
You must have had sex with Lisa at night when she is roommates with Jill and then Lily (both must see you have sex with Lisa at night a few times)
Make Jill your roommate and when Lily joins in the threesome with Jill, keep switching between Jill and Lily, if you've done it right Lisa will come in and catch you all having sex and join in.
Want to know more? there a walkthrough by
Chemmy you can read, it's linked on the first page.