Dear Dhanush,
Please note, settlement of Gift Deed once executed, cannot be cancelled, and even if it is cancelled, it won't be legally considered valid. But only the cancellation will stand valid or it can be challenged before the Court, if -
(i) the Gift Deed was not registered by due process of Law or under proper jurisdiction.
(ii) in the said Gift Deed, it is specifically captured/ retained in a particular clause that the donee (2 brothers) have the right to do so;
(ii) if the possession of the scheduled gifted property is not handed over to the donee (2 brothers) since the date of execution of the said Deed till date;
(iii) if at the time of registration of the Gift Deed, the donor (your mother) was under some provocation to do so.
The cancellation of Gift Deed can only be challenged before the Court of Law, if the above-mentioned points are proved.
For further query, do right to me.
Thanks & Regards.