Blended families

Hi, so I have a dilemma and I thought I’d ask for others advice- I’ve got 3 children, 2 Step children (step son 5 and daughter 7) and a son 3. We are moving into a 3 bed house and the original idea was to give my step daughter a room to herself and have the boys share a room but I then think that’s a room that’s empty for 5 days of the week as they only come over on weekends, maybe my son should have a room to himself? What would you do?