<human>: Give me the gist of the text in a nutshell

Going to get straight to the point. My GFs mother was recently diagnosed with cancer, she will be going through treatment shortly. Her boyfriend of a couple years wants to get married to her, like immediately. We (GF, other family, and I) are worried that in the case of her passing away then he will just run off with her money. He has been married 4 times, and while being a decent human being, he is not trustworthy in this. I could probably have a nice conversation with the man, but would not trust him with more than a goldfish over the weekend. 

My GF is currently trying to get her mom alone to explain this to her, and attempt to convince her to leave her possession to my GF in the case of her passing. That way she can take care of funeral arrangements, pay off her bills, etc.

The first problem is he seemingly will not allow the two to be alone together. So my question is twofold reddit. What can we do to get GF and her mom alone to talk, and what other steps can my GF take in this situation. I am by no means an expert and in fact have absolutely no idea what usually happens in these situation. What do I do.
<bot>: GFs mom has cancer. Boyfriend wants to marry her immediately in case it becomes terminal so he can run with the money. How do we convince mom that this is not the appropriate course of action.