Since the will is challenged by one of them any transfers made during the pendency of the suit is subject to final order passed in the suit. As such it is advisable to not alienate the property during the pendency of the suit. Further in your case since there were only three children to your grand mother and there is a will in force them each are entitled to the share fixed under the will. If your uncle is deceased without leaving any heirs then his share is again to be divided amongst you. The power of attorney that stands in the name of your father is infructuous as the person executed is dead.