It seems like your bf has a big heart, but I'm astonished that he offered your apartment up without even asking you when you pay half the rent. That's incredibly inconsiderate. (There's a breed of very nice people who will bend over backwards to help other people, but end up inconveniencing/sacrificing their partners the most. And the partners are just expected to put up with it because helping others is good.)

I hope your talk with the bf goes well. You really need to establish a plan with the friend and his wife as well. Frankly, I'm betting they stay at least a fortnight unless you're very firm. No matter what, don't let them stay long enough to establish tenancy.