Step son with no bedroom??

Looking for feedback on this as my husband and I have been going back and forth for months!

So, my husband and I live in a 4 bedroom house. I have a step son, step daughter and I had a baby girl 3 months ago. The baby is in our room for now and the other kids have their own rooms. The 4th room is more like an in-law and we rent it out for $1,000 a month.

It’s getting to be time to give the baby her own room and we have been trying to decide what we are going to do with my step son. He 16 and lives with his Mom full time. He has a job now so we basically see him a couple days a month. My step daughter is with us full time and the rooms are too small to share.

We could give my step son the in-law but then we are missing out on $1,000 a month for someone who comes and stays 1 weekend a month.

Help!!! I don’t want my step son to feel like he doesn’t have a home here.