contesting a change in benifiaries in Michigan

Hi...this is a bit of Situation. My husband has had Brain Cancer since 2011. In the middle of June this year he went to stay with his son because i had to work and have teenage children from a previous marriage. I could not be home enough to take care of him they way his son thought i should and talked his dad into staying with him. During this time he had my husband sign power of attorney papers. Towards the end of July my husband took a fall and was hospitalized. He came home from the hospital with me. He stayed home for about a week until he started having violent outburst and with children in the house I coul not allow them to be exposed to the behavior so because he could not be placed in a facility right away he went back to his sons house. Within 3 days of that everything was changed. I no longer received his disability checks to cover household expenses, i was not allowed contact with my husband, the son saying his dad didnt want to talk to me, then on August 22nd the change of benifiarie came through the life insurance website and this is when I found out about the power of attorney. Can i contest the change of benifeary with a shot of winning since i am told he has hours to live and I am not allowed to see him?