My dear Meg, you sound so kind and loving to your husband; that can be difficult in a stressful situation. My patience is pretty thin, so I admire your attitude. But first, have you had time to have a physical yourself? Maybe you need a blood transfusion (bit of humor, but I mean iron pills in the event you are anemic). You do seem to be doing a great job of physical exercise, but second, some mental health help like a therapist could help your distress. Many therapists take Medicare. You have got to be somewhat depressed; your husband is having a very bad time with his cancer and treatments and there's not much more you can do for him. I'm certainly not suggesting antidepressants, just talking to a professional who knows coping techniques. Counseling sure helps me dealing with my pancreatic cancer and my husband's dementia. Last, ask those kids for help; sounds like you go to them for visits which maybe is better as entertaining is even more work. But just let them know you are struggling.
Best wishes and courage, Carrie