Brother in law wants to move in...

So my fiancé’s brother apparently wants to move in with us. His lease is up next month. My fiancé said we could get a two bedroom in our same apartment complex & split the rent. I just don’t know how to feel about it because I feel like his brother won’t contribute. He’s constantly asking my fiancé for money, he doesn’t even have a car so whenever they wanna hang out we have to go pick him up (he currently lives about 25 min away from us) & take him back or we order him a Lyft.

I just don’t want us getting stuck paying a really high rent for a month simply because his brother cannot contribute his half. My fiancé & I rarely fight & when we do it’s because of this situation. There’s times we’re struggling yet he still gives his brother money. There was a time his brother asked for money for his rent & found out it was actually to take his gf on vacation 😒.

I understand that they’re family but he’s 28 years old & he apparently has a job that makes really good money. Idk wtf he’s spending it on. I don’t wanna be bxtch but he’s been trying to do this for almost a year now & idk what to do. I basically told my fiancé to do what he wants & to figure it out but I’m just frustrated 🙄.