How is it your flat. If you own it evict them. If you are renting then move out. They sound horrendous and guess what they arent your friends. A friend doesnt do any of those things, they just sound like bullies, users and abusers. There are nice people out there and everyone deserves to be happy.
Just one point doesnt all this get tiring and a bit dull. Take a step back, take a deep breath and get away or move these people away from you or there will be more endless drama. If you cnat help yourself go and spek to your parents or the GP or welfare services. .
What are the downsides?