Is there anyway you can have sex with the mom's friend who comes over drunk?
There's multiple ways. When you get the scene of Maggie (Mother) and Sophie (Friend) at the table, how things play out depend on a variety of factors.
You need to abuse the rollback system to get Sophie's inhibition down to 60 for full sex. At the table scene this happens when your dick is exposed to her by Maggie. For good alignment I think at first you have to give her your bed and will automatically sleep on the couch. When she gives you the kiss goodbye whatever stat raises/lowers abuse the rollback system to help that along. Stats that lower aim for 60, stats that raise aim for 70. Bad alignment path doesn't need any of this since she's passed out.
GOOD ALIGNMENT (70 or more): You drop Maggie off to bed then come back to the couch. Choose to take Sophie to your room. She'll wake up, ask you to stay and help her get naked, you'll take off your shorts too. She starts to jerk you off in her sleep. If you don't wake her you come and lose an alignment point. If you wake her she'll have sex with you.
BAD ALIGNMENT (30 or less): You drop Maggie off to bed. If you have the Incest flaw from the Mind Control power you have three options: Just the tip (rape), Teach her a lesson (anal rape), Leave her alone. She sleeps through whatever you choose to do. When you go into the living room you have the option to go to bed or look closer at Sophie. Choose to look closer and whenever the choice prompt comes up pick the second option. You'll uncover more of her body then eventually rape her in her sleep.
MAGGIE & SOPHIE: If you have the Incest flaw and have given Maggie the Obsessive mental illness then Maggie will hug you and will expose your dick to Sophie. Sophie will blow you with your mother's encouragement and Maggie will kiss Sophie after you've come to taste your semen. Then Maggie will leave and Sophie will bend over the table and tell you to fuck her. She passes out after and you dump her naked body on the couch.