Disowing daughter

I'm 70 year old widow, my son live with me,after stroke i,m unable to move without any help.the assets and property belongs to my husband.To take care of me , my son remain unmarried .the problem is my daughter having a son ( who took divorced from her husband without alomony ) living with us and took money fom me for their day to day exp.but both of my daughter and her son took drug and on lavish lifestyile they asked more money from me and my son and always threatening if we refuse to pay money they will go police station do a fir on domestic violence ground against me and my son.so we paid them , now our financial condition is poor due to fulfill their day to day demand .but as their demand is increasing day by day they want to let me die soon so they can take the property and sell it off and threatened that after my death they will go to police and do fir stating that my son is ( who loves me and taking my care) killed me ,so that police will arrest my son in future and they(daughter and her son) can enjoy the whole property without any hindrance. now i want to take any step which will help to protect my son after my death from this cruel intentions of my daughter and her son....please guide me .