Father's property settlement between two wives and children

We are Muslim by religion. My father had two wives and my mother is the second wife. After my fathers unfortunate demise the first family children's took over all the property and refuse to share our rights. My father left behind a flat and a major share in a restaurant in Mumbai with several other property in our village. I seek expertise advise as to how we should gain our rights for the above said properties. My fathers first wife had 4 son and 2 daughters out of which one elder son has passed away. The second wife that's my mother has 3 sons Please help me with the proper guidance. Regards