rights of 1st wife and children in property-muslim law

I am a Muslim. My father has 2 wives. I am eldest and only son from first wife and there are 4 more children( sisters). 2nd wife has 3 sons and 1 daughters. My father ( no more now) has made a will assigning his ancestral property to his 4 sons and his 2nd wife. Management rights of the property has been assigned to his 2nd wife and one of her son. Keeping in view 2nd wife's past behavior towards children from 1st wife, we are of the firm view that she will be usurping the entire proceeds from the property and will not be giving us our share. What legal remedy do we have to nullify the will , and claim equal share from the property ? Secondly, there are few properties which have been bought by my father ? Do children from the 1st wife have any claim on those properties which have been bought by my father ? Kindly advise.