I believe that Lillian was a very poor mother for Robert. He needed a strong person to help him -all Lillian did was cater to his illness. She made the right decision on not letting them do a lobotomy on him.
No the tapes did not change my mind on Robert. What he may have been seeing was probably not what his sister saw when she looked at the tapes. His illness was full circle. Had he had a mother or family that really cared about him they would have helped him - gotten him the medication that he needed and saw to it that he took it. He could have had a decent life, but ignorant, weak family took that from him. His mothers weakness was not helpful for him.