Right of sons in ancestral property when father remarry

We are two brothers and two sisters. My father has received money 3 years ago from my grandfather and equally divided among three brothers including my father. The money they have received on account of appeal of farmers land from U. P. Govt. (land was taken by Govt. 20 years ago). My father has purchased land from part of that amount. My mother has expired 9 months ago & father has marry to a girl now and we have opposed that. Now my father are saying that he will not give anything (Village House, purchase land & others) to us and it is come to us that he have done a will either in name of that girl or any other. Also one property is in name of my mother How will be distribution of that property? I want to know: 1. What is our rights in that property & how we can claim that? 2. If that girl give birth to any child than what will be the effect? 3. What steps we should take immediately?