If the property in the hands of your grandfather was self acquired then he could dispose it by any valid/registered deed in anyone’s favor.
If said Bakshish Patra stands for;’Gift Deed’ of immovable property and property disposed by it is self acquired and gift is accepted by done then the gift is complete.
It may be futile and waste to contest it.
If your grandmother (your father’s mother) is alive then she can dispose her estate/property in her life time by any valid/registered deed in anyone’s favor.
No one has any forced share in it, be it your father or uncle.
Grandson/daughter/child has NO forced share in any estate/property of grandparents.
If she deceases without disposing her estate/property in her life time by any valid/registered deed in anyone’s favor then it shall be open to succession per applicable succession laws on date of death, a hint of which is given above.
Your grandmother can dispose by her sweet will in her life time by a valid/registered deed say; settlement deed with life rights/Gift/sale etc etc ….even WILL.
It is better if WILL is registered.
Any WILL can be contested.
Rest you may discuss with your own very able LOCAL counsel of unshakable repute and integrity specializing in such/revenue/civil matters and personal law that applies in your case and having successful track record.