Ancestral property succession open - rights of grandchildren while parents are alive

Your children are entitled to a share out of your share in the property equally at par with you.

Therefore you and your sister can partition the property into two shares by a registered partition deed and thereafter you can partition your share of property with your children.

The share allotted to your sister will become her own and absolute property hence her children don't have any rights in your sister's share of ancestral property.

Presumably you are professing Hinduism, hence both of you (yourself and your sister) are equal share-holder of the properties left behind by your father.

Children of both of you has no right, interest or claim in the properties of your father.

It would be better to draw a registered family settlement amicably.

Children of both of you and your sister have no right to  claim any share in properties left by your father. 

You and your sister have equal share in properties left by your father better executed register family settlement..

You and your sister have an equal share in the property and go for partition deed.

thank you sirs

You are welcome for understanding and appreciation.

Facts posted do not suggest the property to be ancestral. Grandchildren of the deceased have no rights over the property.

Here since the property is ancestral the normal succession rules will apply it will go to class one heir only that means to you and your sister grandchildrens have no right to inherit as of now.