Is it malpractice for an attorney to withhold documents from the opposing client knowing it could benefit them and their case?

our father died in a house fire in May of this year. Everything burned to the ground. The will was rewritten for my fathers new wife of two years. It was written poorly and many problems have been stirred up because of it. Many things were removed from the property by his new wife and family and we were told she had the right to it, she is executor. However we found documents that state that my sister and I were and are the Beneficiary Bill of Sale in 2006 which was not changed. The attorney who wrote this document for my parents is also the one who rewrote the will for my father and his new wife. Although he presented us with the new will he never gave us the documents for the Bill of Sale. The attorney has permitted her funds for the loss of things that were never hers to start with.