We have recently helped a number of elderly clients suffering from Dementia and in care in Australia remain with their close relatives here.
The Department does accept that in these circumstances, where an elderly applicant is in care, it is considered treatment and a medical treatment visa is available. Generally in these circumstances a 10 year visa will be issued.
If the applicant is otherwise incapacitated and cannot travel due to age, then a medical treatment visa should also be available. These applications of course need to be supported by strong medical evidence.
For specific advice and guidance tailored to your situation, ask an immigration expert a question at your nominated cost here. You can also get a DIY migration kit specifically for Onshore Aged Parents Visa (804) here.