What sleeping arrangements would you choose for this step family?

It's for a book I'm writing. The main character who's a 13 year old girl has two sisters, 15 and 9 and her mum marries a man with a 13 year old girl, and two sons, 7 and 11. Who would you have sharing a room in a normal 4 bedroom house. I'm not interested in whether it's your sort of book. I've got the storyline, I'm just sorting out the logistics and trying to make it realistic.