I have 2 dc with dh 10(boy) and 12(girl) and he has a son from a previous relationship (23) who always lived with his mum but we have always taken him out at the weekend.
His mum has a 2 bed house which he had a bedroom at and then she had a daughter with her current partner who slept in their room until dss moved out and rented with a partner, then they moved their dd into his old room, by this time she was 7.
The relationship didn't work out and was over in about 18 months but when he split from his girlfriend neither could afford to stay in the flat so dss asked if he could stay with us as his mum had given his old room to his sister now.
We agreed thinking it would be temporary but we didn't have a bedroom for him so put our ds and dd in together for the time being freeing the small room for dss.
Now dd is getting older and going through puberty she's resenting sharing with her brother, he also has SEN and they are constantly bickering and she clearly needs her own room as they don't get on at all.
dss has been back just over a year and is working so could afford to move out, dh thinks it's not fair as it's his room and not his fault the younger ones fight.
He also hasn't had the opportunity to live with his son before as his relationship with his mum broke shortly after Dss was born so is enjoying having him around.
I don't have any issues with Dss I have known him since he was small and love him to bits but I don't think there's room for him here and it's not working for me or our children.