you did not mention in your query that property is owned by your grandmom
for revocation of settlement in your and your sister's favour, your aunt will need proof/evidence to prove her allegations
even if she files some case and files an interim application, for that too she will have to show a prima facie case for getting an order of status quo
was the settlement deed a registered document?
if you fear that your aunt will take any adverse steps against you and have the settlement revoked then you can file a declaratory suit in court to declare you and your sister as 50% owners of the property and claim consequential reliefs. As an alternative you can also claim partition with the condition that you will take care of your grandma and her basic needs
you can narrate the attitude of your aunt and your relatives in trying to prevent you from meeting your grandma in your plaint