I am 62 and am diagnosed as manic depressive and have had 2 hospitalized breakdowns in last 3 years. At one time I was primary long distance attendant (live 500 mi from parents). I can no longer contribute to their care. Sister lives within 35 mi and has assumed role. Parents are able to do daily care at home as long as they have each other to call upon. Sister takes them to all dr appointments and does shopping for them. They have someone come weekly to clean house, bedding change, organize, etc. Goodness I could go on and on. I just need help. They are aware of my illness and know I recovering daily. But I cannot help and I don't know how to tell them.
You tell them what you've told us. That you are not mentally or emotionally capable of participating in your parents care. They know about the illness so you shouldn't have to go into a big explanation about your inability to participate. If you had a physical illness your family would take that into consideration. Just because you have a mental illness doesn't mean that it's not still ILLNESS.