Probably confusing
An adult needs to get involved and help these kids out. Whether or not you think they are doing it for attention is besides the point, there is something wrong if someone is actively hurting themselves.
There is never a single reason for self harm, it is always a lot of everything. It's not "oh a boy rejected me" it is literally everything.
I p......
Criticize their shrine, probably. "THIS is the best selection of pictures of me you could possibly choose? This one makes me look fat, change it. Why would you use my favorite underwear for this?! I've been looking for those you idiot! And what the hell is this? A lock of my HAIR?!? When did you cut that, what the hell?!? And another thing-" etc et......
First off, boundaries lay down your boundaries. Figure out how chores are going to be handled and make sure every roommate is on the same page.
I think I have too bad roommate stories one of them was when I was in college and I moved in with this girl who had two kids and I was paying her money every month to live in her house. I still had to buy ......