Can my grandmas significant other change their will once she dies?

My grandma is not doing well and is sadly likely away to pass away soon. She told us when she found out she didn’t have much time (about a month ago) that she wanted to give everyone in the family their inheritance money before she died. Then she changed her mind which is completely fine, it’s hers.

Lately she’s been declining and is staying at home with home care in a hospital bed. My mom reached out to my “papa” asking for updates of her prognosis and he was extremely rude and told her it was not her business to know(that’s literally my grandmas child, it is definitely her business) and said to her “you aren’t waiting for answers, WE ARE” (in caps like that)

He isn’t my real papa but I’ve always thought of him as one because I haven’t seen my bio grandpa since I was like 5.

And he is a great guy usually but how he talked to my mom I’m just taken aback.. I was already somewhat worried that when she died he would vanish out of our lives. Now I’m finding out that she actually changed her will to now we get it when *both* of them have passed. He has like 15-20 years on her and as I said I’m already worried he won’t even try to be part of our lives when she dies. It is her money from retirement, money she had before even meeting him, inheritance from her mother and her profit from the vacation home they sold.

Can he go and change the will when she dies or just spend all the money for himself? I know it’s not about the money but if he did that she would be rolling in her grave as this is something she’s worked hard for, to be able to leave something for us and she’s told me that for years.

Not only all that but since the plans have been changed, she has been a little out of it on medication, not making sense half the time, so I’m scared he took advantage of that and convinced her to change it . Maybe I’m just paranoid ..

We just got more bad news about her today and I just needed to vent. I can’t talk to her about it because as I said half the time she isn’t totally “with it” lately and stress is the last thing she needs.