Pregnant and my SO wants his brother to move in.

Claudia
I don't mean to sound selfish but is it just me?!
I'm 23 soon to be 24 in one month I'm 7 weeks pregnant and it's been a high risk one.
Well we are in the process of finding a home to raise our little baby in. 
Recently his parents offered us to rent their second home from them which I'm more than ok with!! But my SO keeps
Insisting his brother and gf move in with us.
Because his parents want them desperately out of their home. Simply because he is a 22 year old that doesn't help around the house and all they do isSleep go out. So their parents decided it's up to my SO to step in and help him become responsible. 
This is were my issue begins as a pregnant 23 year old I don't want roommates and I don't want to babysit his brother and 18 year old gf who can't maintain a job because she keeps getting fired. My SO doesn't understand that having a baby is going to be hard the first few months I need to be able to walk around the house with a tittle hanging out feeding my own baby or waking up at 4 in the morning to prep a bottle for my kid without having to quietly sneak down to the kitchen with out being loud or turning on lights.. Idk if it's just me and I'm being selfish I just know how they are and don't think it's time for us to take care of them too :( 
Any advice ladies :( please don't be so harsh on me if i do sound a bit selfish I also have two brothers and understand where he is coming from but I just don't think the time is right not with a baby on the way