life-estate reversal

What is the name of your state (only U.S. law)? New york
Can breach of fiduciary duties constitute a reversal in a life estate? My brother stole all my mother's money via POA after my father died and mother didn't even realize she had deeded house to him prior to my fathers death.

Your post is rather cryptic.

Is your mother still alive? Is she still legally competent?

The POA that you mention... Your brother was the agent/attorney in fact for your father or your mother or both?

The life estate... Your bother deeded the house to himself, leaving a life estate to your mother? And he did that as your father's agent? And your mother was a co-owner of the house or the sole owner? And she signed the deed transferring ownership and creating the life estate?

If your mother is still alive, has she contacted law enforcement concerning your brother's actions?