Dear Querist
There are various laws that governs the appointment of Guardian of a person with disabilities, like The National Trust Act for the Welfare of Persons with Autism, Cerebral Palsy, Mental Retardation and Multiple Disabilities Act enacted in 1999, the Mental Health Care Act that became a law in 2017 and the Rights of persons with Disabilities Act made in 2016
but It involves several disputed questions of fact. First one is whether the person is suffers from dementia. The second is the nature and extent of dementia and the third is whether he is incapable of looking after his own affairs,"
In a Judgment passed by Bombay High Court it was said the judges. "Only because a person is suffering from dementia, one cannot come to the conclusion that he is incapable of looking after his own affairs. It all depends upon the nature and the degree of dementia. These are the matters which are to be decided after considering evidence of the experts and doctors,"
File an application before appropriate court and then lead evidence and get the order from the court