Hi Dawn,
Do you think that Mum is frightened of losing the company he provides, is 'brain washed' (sorry for that awful term but can't think of another at the moment) by him, or doesn't realise that she does not have to look after him at all.
I wonder if a visit to an appropriate solicitor would shed some light? Maybe a letter to the daughter suggesting that he owes for his keep. However be wary. I don't know the law but perhaps as his current status is as a 'guest' in your Mum's home makes it easier to get him out than if he was paying some kind of rent. Be very wary, because if Mum is under his influence at all, then who knows what he might ask her to sign?
Is that POA for Mum activated?
At the very least talk to Age UK or similar. IF he left and Mum was initially upset, do you think she would soon forget or do you think she is desperate for 'someone' to be there, however anxious it makes her? Are you able to get Mum on her own and have a good chat about things or is he always present?
The daughter is in clover. She has no responsibility, no expenses and presumably will benefit from the sale of his old home?
They both, father and daughter, sound like 'users' from what you have posted.
To be brutal, but honest, things are only going to get worse. Inevitable.
You need professional advice and need to act soon.