Mother's Property

I have an elderly mother nearly 90 and my eldest brother mentally weak is helping my mother. We have made adequate arrangements to look after them at their home. My late father has given a vacant site to her and also had an understanding with my youngest brother that the house they are living in now will go to him only after their time. The title was transferred to his name some years ago on the above understanding. I am currently overseas and my wife is stuck in India due to COVID pandemic. My youngest brother is sending threatening e-mails to me that if I do not agree to give GPO to my wife to sign the documents to sell mother's vacant site he will remove the mother and the weak eldest brother from their house and drop them at my house at a different city. How do I deal with this sort of situation? Can children sell mother's property? I am really worried because my wife has to travel. I would appreciate your professional advice. Regards, YRK