How to secure senior citizen's property legally?

I seek legal advice regarding the illegal possession of my maternal grandmother’s (Nani’s) property and her abuse by her grandson. My Nani has three children: my mother, my aunt, and one son (Mama), who became mentally and physically disabled after an accident. Nani supported Mama, my abandoned aunt, and her son (S) for many years. My mother lived separately after marriage. Around 2019, S began harassing Nani and took control of all her property. He even admitted her to a mental hospital, after which she lost her speech and mental awareness. In 2021, my mother brought Nani to our home and has since borne all her medical and living expenses. S continues to occupy Nani’s property without legal authority, provides no support to Nani, my aunt, or disabled Mama, withholds all property documents, and threatens us. We seek advice on how to evict S, recover property documents, protect Nani, and ensure that her property is legally secured for her lawful heirs—my mother, aunt, and Mama—under applicable civil, criminal, and senior citizen protection laws.