My mother in-law is considering letting her 30 year old sons 35 year old friend move in with them?

My boyfriend (her good son) and I live on our own now. Her almost 30 year old son does not. Still lives and home and recently asked her if one of his buddies can move in for a bit until he gets some.things figured out. He's a 35 year old guy and has no where to go cuz he got kicked out of an apartment with friends who didn't pay so they all had to leave. Anyway it's only gonna be a temporary situation until my boyfriend's father comes back home (he's in the hospital). She asked what we think about the situation. She knows I don't like her older son and the brothers don't get along to well (his brother has a drinking problem). She said the guy seems nice, doesn't drink or smoke (he must or he wouldn't be friends with her older son, he doesn't have nice friends) and she needs help money wise. I honestly don't think it's a good idea seeing his older brothers track record of friends who party and steal. I could be wrong but idk. My boyfriend isn't sure about the idea. And his dad also has no clue this guy is moving in (he apparently doesn't need to know). His grandma and everyone else says he seems nice and it would help his mom out..it's her house she can do whatever she wants. But I just want some advice on how to tell her I don't think it's a good idea.