Property

You need to register the GPA and on this case the Ld.Registrar has to be called to your place, invoking the special provision with the prescribed Fees.

Yes, you can make a GPA and you made it registered by notray. Or you can make a proper will of her and registered to registrar office. After that you can do what ever you want.

1, you are the legal successor in your ancestral property so after demise of your mother you will have legal and sufficient right for the same property

2, you do not have to go for GPA  

Sir, 

its a property dad earned out of his savings & got it registered in mom's name, dad passed away 

as they didnot have any kids of their own,

her younger sister had 2 sons out of which 1 kid was adopted & brought up which was me but nothing is in writing or legally documented.

now that she is in bed ridden due to cancer , my sibling is claiming share equally with me as they dont have any property of their own and they are staying in rented house.

how to handle this,  

1, well i got it but after demise of your mother the GPA will no longer valid

2, its better you make a WILL (VASIYATNAMA) in your favor in presence of two proper witness and same be executed after demise of your mother

sir, 

mother is alive but she is bed ridden

i have already executed a gpa favouring me with notary seal & sign both of us in front of a advocate

my query to you was is the gpa valid even after her sudden demise