the land is divided among my uncles fathers but it is undivided between his sister and him
so cant this be an ancestral property now.
This means that she is having an equal right in the property held by him now.
Therefor to avoid litigation or any other problem in the future, he can better talk to his sister, arrange for a mutual partition or any other arrangement by which she shall be compensated in lieu of her share in the property, get a registered relinquishment deed from her and afterwards can execute a registered gift deed in yor favor which will be more perfect legally without having to face any legal hassle in the future in this regard.
so if his sister moves to the curt then what will be my situation and what should I do to over come this situation in future.
Ask your uncle to give her share or give money in lieu so that the problem can be solved now itself instead of postponing this problem for a future date spoling the future peace.