Sorry to hear both of your troubles. It is hard to watch our old ones as they near the end. I currently am dealing with a 13 year old lab who is failing bit by bit, but two years ago lost my 14 year old Akita cross Shadow.
Shadow also had hind end weakness, but hers was due to arthritis, it ultimately went to her spine and we knew it was time. We tried many supplements and shots, and drugs, and each worked for a time but ultimately would stop being effective. In the end it came down to trial and error to see what helped to keep her comfortable and mobile. They are so dear to us aren't they.