Hello from a former caregiver. One suggestion is to help with weeding/clearing brush with your local park district or forest preserves like we have here since he likes to be outdoors. The problem is that you would have to go with him and I know that would be difficult with caring for your mother who also has dementia.

If you don't already have help coming in I would strongly suggest you do that because you will surely burn out from caring for both of them. You need to be able to get away once in awhile for lunch with a friend, a walk, whatever you enjoy in order to take care of yourself so you can take care of them.

Blessings to you and your family. Ruth Ann