Taking care of senior citizen parents

Dear Exparts, I am a senior citizen aged 78 years and my wife is 71 years. We have two children, one son aged 45 years married, and his wife is about 34 years, having a child aged 6 years. We are from Kolkata, but now living with my son in Bangalore since 14 years. My son is married since 7 years. My daughter is also married and living with her husband in Bangalore. Earlier we were living in rented house, but recently my son has purchased a flat in Bangalore in the joint ownership with his wife and we are living together there. My flat in Kolkata has been sold out as none was interested to maintain the property and I was unable to maintain on my own due to my financial constraints, since neither I am getting pension nor having other source of income. I had lost my entire retirement benefits in investing in a business for my son when he was not having any job. My wife also has no source of income. We are purely living on the mercy of my son. We were a very happy family. Recently, my daughter-in-law started misbehaving with us probably in a bid to replace us with her own parents, herself being a single child. We are being treated as beggars. My son is reluctant to do anything may be due to pressure being created upon him. We also apprehend some of their recent associates who are triggering from behind. We are feeling very much insecure at this frag end of life. Please advice.