I think you need to keep repeating that this was her idea, she started this ball rolling.

Do not sleep with your mom. That is completely unreasonable. Having separate rooms would be a compromise, plus really, sharing a room is a bit overrated, having your own space to come into when you need it is pretty important. You can always visit each other.

Pick a rent that you think is reasonable and stick with that.

You're in a transition where your mom may be experiencing memory loss. That's a pretty major thing to forget that you said, inviting your daughters bf to live with you. Know that if this continues you may be taking over more of the management of your home if your mom's memory keeps failing.

So start here. This isn't up for debate. This was her idea, there was some aspect of this that appealed to her and now something that is scaring her. Maybe, start appreciating her, once your bf has moved in, make her feel good and having a him here to help. Keep a happy banter with her, old style courtesy. Share meals together where she's included in the conversation. Ask her questions. Let her enjoy the three of you living together.

NTA