YEP. I think that's a good solution! Cuts out all the stress really.

However I just wanted to point out that it is highly likely that SDD won't move out the minute after she turns 18. Or she could come and go a little bit iykwim? I imagine you would always want to have a spare bedroom available to her JIC, and its not like a 4 bdrm house will ever feel too big.

Also, I think you need a bit of a break from the house tbh.