How to help a parent who is attempting to be the caregiver for a grown child?

It is beyond their ability & means. Female over 80 with poor vision, hearing, and mobility. In the past 18 months husband was moved to a nursing home as a result of a stroke, eldest son lost hard fought battle with cancer and has another son that has been living with her for some time and has developed a long term illness. She had relied on the son living with her to provide some assistance in the past. Now she is being drained not only financially, but more importantly emotionally as she attempts to be his caregiver listening to his needs, problems, ongoing moaning and screams in pain, inability to clean up after himself, etc. Other family members are concerned and unable to persuade her to seriously consider other options. She is emotionally frail and "monitored" in all actions and discussions by the son that lives in the home. She is suffering from caregiver burnout that may be bordering on elder abuse.