hello!!!
For the fourth star you have to do the normal polyamorous route, and give them the lemonade to drink. This will make the vanilla room dirty. Then you must hide Shadow in your room, and accept that he goes with you. To finally tell Vanilla to share a bed with you.
For the last star, you must be on the shadow route and when you are opening doors, before you talk to vanilla you have to touch the upper right corner.
And that's all, I hope it works ^^
Sorry if I had any mistake