Gift deed cancellation. and the posessio. clarification needed.

Hi, my father had 2 brothers(elder and younger, my father is the middle one). Since elder brother didnt get married he gifted his property to his one of the younger brother's son. Donee was minor at that time. To raise her sons she had made agrement with me on this land and took some amount saying the propertywill be registered once her son become major. In 1991 donee,major son, had registered the property to me. Turning point is just before this register the doner had revoked the gift deed.and doner was the witness for the registration too.. he intentionally cancelled the gift deed and keeping it silent he signatured as witness for my registration. Now the doner and donee both are not alive. My cousins( my father's younger bother sons and my own brother) claim that tgis registration is not vakid as the gift deed was cancelled before myregistration.and they are the leagal hairs of donef and they want the equal share in the property. Now my question is, 1.does this cancellation legal? 2.what about the registration done with me?