AS mentioned by you the property is your G M's name. So she has a right as mentioned in (2) below.
For your general info, I am sharing the below mentioned info.
1) If the property is in your G.F's name, then your G.M only has a share in it as do your father, his brother and sister. (The property will be distributed among them)
I2) f the property is in your G.M's name, then she can give it any one she likes while she is alive by sale or Gift. Or She can bequeath it to any one individually or jointly by her will.
I3) f your G.M'. is a co-owner of the property, she can do everything as described in point (2) but for her share only. As for your G.F's share, it will be distributed as mentioned in point (1).
4) The law applicable will be HSA for point (1) and ISA for point no. (2)