About a Property!

My grandfather have 5 children 3 sons and 2 daughters from that one is my mom. My grandfather is having 2 properties one is where he was living and the other is on tenant which is some what 5 minutes of distance., his 3 sons are so greedy and so cruel in nature..my grandpfather wanted to give his property parts to his 2 sisters from which one sister was my father’s mom.,but because of his sons they kept quiet and my dadi left this world and the other one she kept quiet too., my mother was the elder one after one son., so what grandfather did is he sold the second property to my father in 2005 in 4 lakhs which was 100 Ghz he trust my farher and adore him so much more than his sons., no one knows about this registration except my grandmother she was present at that time.,my grandfather died few years ago.,my grandmother was quiet till these many years but after my marriage about one year ago she started cursing my mom to give half of the property to her younger daughter..,but my mom refuse to because she was living in a rented house from many years and my aunt was having her own inlaws house which was 250 Ghz ., my grandmother is torturing my mother and blackmailing her if she will not give the half of the property I can do different thing! She also broke the relationship with my mom because of his greedy sons! My mom is a heart patient., in a month once or twice my grandmother comes along with her sons and start shouting on my mom they are giving trouble in her life.my mom’s elder brother can make illegal and fake documents by which grandma can take his help.,my mom wants to give 5 or 8 lakhs on behalf of property to her sister but they refuse to take so..what should be done please explain??? I can’t see my mom like this...