Power of Attorney in TX

My husband and I have power of attorney over his mother which is incapicitated. My brother in law had the POA, however, due to family issues the POA was changed over to my husband and his brother\'s was revoked. This angered my brother in law and several other siblings. Long story short my brother in law has been threatening a lawsuit and telling financial institutions and the post office that we have obtained the POA unlawfully. Nothing has come of it as of now, at least not that we know of. How can we stop the harrassment and how can we get him to turn over financials docs that belong to my mother in law???