Here's a small wt for the sleepover. Just some steps I remember, if anyone wants to do a more professional wt, be my guest.
1. To start the whole process, you need to have stolen Martin's flashdrive (when he is in Maria's room). To trigger this, you need to talk to him when he is alone at the pool. Then give the flashdrive to your pal at school (forgot the name), wait a day, meet with him and Ako at 18:00 and spy on Martin. Then you have to talk to Martin again at the pool. This is enough for the sleepover event chain to start, you don't actually have to decide yet if you want to give the flashdrive to the girlfriend or befriend Martin. He actually leaves both girls alone either way, even when you befriend him, so it might be a good idea to save here to see what Walkius has planned for the friend path.
2. Now Ako should initiate a talk at school. All you have to do now is get the booze and eat with the group at school (you probably need enough reputation, but if you used an old save you should have more than enough already). Alice should ask the mother for permition during dinner.
3. The first sleepover is Friday night at 22.00h. Later you can have sleepovers during the week. Do NOT do anything at 21.00h, there is a bug. Instead use the "wait an hour" button.