As far as ownership and possession rights go, where do I stand if I am a joint tenant?

My mother and I have a quit claim deed naming her and myself as joint tenants with full rights of survivorship for her property. I am also named as her beneficiary in her will to her estate with the exception of a few things that go to my siblings. She is now in a hospice home. She named my brother as her POA in the event she can't make her own decisions. He went to the city two weeks ago and paid her property taxes and quit claim deeded the property to himself then to himself and his wife as joint tenants. My mother did not want this. She wants me to have the house. She is revoking the POA and naming me as her POA in a few days.