Hi as the doctors have mentioned it's probably very normal for his age. You have always seen an active athletic man in him that it is hard for you to accept that he is growing old. This also doesn't mean that you have to let him get old and do nothing about it. Maybe it's not going to be possible for him to get on his bike all over again or run a marathon but he can still do things that are safe and appropriate for his age. He needs to be spoken to a lot. Keep him company let relatives and friends come over and talk to him. If there are kids even better. It'll get him out of his depression and feeling of worthlessness. Let him do small chores around the house. Walk around the neighborhood. Play some games on a phone or solve puzzles if he is interested in that kind of things. He can involve himself in listening to music. If he wants to go outdoors it's always better that somebody accompanies him. As he has imbalance he can take a walker with him. The options are endless you will just have to figure out what works best for him. It's a slow process. With respect to his tremors if it's hindering his activities he can definitely get medication for it (but not without side effects) you can talk to your doctor about it as they are prescription medications. Sometimes old people are like children and they have to be taken care of like children. At this time the support of his family is what he requires the most more than any medication. I wish your father good health. Take care :)