1. Your aunt's claim for her share or compensation in lieu is not legally maintainable. She cannot approach court at this stage if she feels that the gift deed was obtained fraudulently especially after three years of this registered transaction, it is barred by limitation and also since the donee is not alive she cannot file the case against the legal heirs at this stage, even if she files any case the court may not entertain the same for the above reasons or she may be fighting a losing legal battle.
2. You were advised to file a partition suit to claim your legitimate share in the property with separate possession, there is no time limit for filing suit for partition.
3. If in future they claim and their claim is approved by court then you may have to give their share proportionately if you are going to take their share also now by operating the said law.
4. You do not have any rights to sell the share of your missing uncle in the property, if you do so then it is illegal and the registrar would not allow you to sell the share of your missing uncle without a death certificate and legal heirship certificate.
You may better confine to your rights alone in the property instead of becoming greedy to sell his share also without any rights and get into a deep trouble in future.