Grandfather's Self occupied property

My grandfather has got a house on his own work. He has two sons. My father is younger one and he died when I was 4 years old. Before his death my grandfather has registered the house in the name of his sons stating "after my death the house belongs to my both sons" After few years my father's brother has registered the house (as my father and grandfather both had died) by making it two parts allowing one part to his childrens and other part to me and my brother. This all happened during 90's period. Now my sister is claiming that she has share in the house and the income from hpuse should be shared by three I hope you understood the problem and my doubts regarding this are 1) whether this property is ancestral property?? 2) Do my sister's claim is valid as per law ?? If yes, on what basis ?? 3) Do granddaughter has right in grandfather's property or only grandsons property ?? 4) whether my sister signature is also required when we sell the house ?? If yes, What we can do if she refused to sign unless she has been given share in the property ?? 5) Can my sister's son claim the share in case my sister died ?? Please clarify..