Sorry you're going through this.
What to do to extricate yourself from the trio?
Stop calling them
When they call take longer to answer, delay returning their calls till next day r the weekend. This will start to signal to them you're not really interested in their conversation.
They will intensify their efforts in trying to contact you! just keep being polite but brief. if they say they're coming over toyour room whatever, either tell them you're meeting up with someone or invite some other people to your room so when they arrive they don't get the chance to dominate you.
Whatever you used to do to hang out together, stop it! desist from going at the same time. Change your schedule. Be proactive and find new people to walk with in the interim to lunch, activities, parties.
If you bump into them socially, always be light hearted and brief
Don't bad mouth them to anyone, avoid any drama.
They'll soon get the message and find a new pawn.
Be vigilant! they will try and wear you down, they'll might even be more kind & inclusive towards you and you'll wonder whether you're being harsh. It's all part of the ploy because they have long enjoyed you're part in their narccisstic games. Stick to your guns and don't get sucked back into this toxic 'fiendship'.