My socially active MIL has been making extremely bad financial decisions and has now been "romance" scammed, online, three times. Most likely by the same "famous" person that disappears when the family finds out and reappears as someone else a couple of months later. Now she has asked for a separation from her spouse (he is aware of the issue). She controls all of their finances and refuses any and all interventions by loved ones trying to protect both her and her assets. She reacts with fury that anyone should question her.
Then he can file for separation and the attorney can help him separate his finances from hers.
Divorce is expensive and stressful and there will be nothing like her getting smacked in the face with reality…. She may very well be blindsided, then you all might be able to figure out if this is mental illness or dementia.
There may be little that can ultimately be done by this. Were I the spouse I would see a divorce attorney for legal division of assets and separation, and that even were I to stay in the home with the spouse. That will be crucial for his protection. As to the rest of it, there won't be a likelihood of winning conservancy or guardianship. It is worth seeing an attorney about.
I myself would begin with a call to, and discussion with APS. You can SKIP all the discussions and attempts at convincing this woman that Brad Pitt is not in love with her. You won't succeed and it is a waste of energy.