Changes in will

My father passed away and one year ago he made a will leaving me and my brother as beneficiary. Two months ago my father was diagnosed with Alzheimers and another sibling took him to a lawyer to get a power of attorney
for himself but he also changed the will completely. Even though my father at the time of this change could not write or speak his name so that had to go back a few days later and at the prompting of another sibling( Who was not in the original will) completely changed the will to include himself, wife and others.
This week was made one week prior to his admitance to a nursing home with full blown Alzheimers. This has all taken place in San Diego CA Could you please advise.

That new will can be voided by a court if you show that he was not competent.

That is fraud basically.