she may challange the will on different grounds alleging fraud or forgeryor undue influence by your father or uncle by getting executed the will.

for safty measure, if you or your family is doubtfull about the intentions of your aunt, you should ask your father or uncle to get transfer the ownership from their mother during her life time. its just like sale deed.

how ever if you do not want to do this, then you shold also get a sworn affidaivt from your granmother regarding attestationof will duly attested by the magistrate.

A will can be challenged on various grounds. Guessing such grounds may not be worth. Cross the bridge when it comes.