Can this will be successfully contested.

My 87 year old uncle changed his will that had been in place for years. He had undergone major surgery 2 weeks before the change and lab work done one week after the change indicated kidney failure. He was afraid of being alone and confused. He left his entire estate to his baby sisters kids. He always said that he would not leave them as much because they were already rich. The family feels like that he was persuaded to do this by being told that he would have to go to a nursing home is he didn't. We feel like there was undue influence in his decision to change his will because the rest of the children were always told by him that his estate was divided in 9 equal shares not 3. No one was aware of this change until his death and everyone is in a state of shock because this is a multi-million dollar estate.