My 13 year old stepson stays with us 12 days a month my 11 yr old stepdaughter stays with us 8 days a month our 1 yr old son is with us full time is it OK that I gave him his own rm and have my stepkids share since they are hardly with us? They said they don't mind.

I see nothing wrong with that at all.

At those ages its not OK. They are of an age that they both require privacy. It would be best to keep the girl and boy separate. You son could share some space in his room. So the boys could share a room and the girl gets one of her own. Or think about moving to accommodate all the children.