Grand Father Property

My Grand Father bought total 3 properties. He had 4 children 2 Sons & 2 Daughters - All of used to stay in the property which is on the name of my grand father, rest 2 properties were on the name of second son & first daughter. those 2 properties were bought by my grandfather in municipal quarters alloted on luck draw basis he was applied on the names of 4 children but only 2 were alloted. after his death those 2 properties which were on the name of second son & first daughter they sold those properties and purchased somewere without leaving any legal proof. now the house in which all of them used to stay is still on my grandfather name, I am the grandson of first son to my grandfather. now the documents of property is with me. my father & mother also passed away. now we have only shelter is the present house in which our grand parents. my father & mother stayed. now second son & other daughters asking for house settlement. please advice what is the share to them will get. can we proceed for legal action on those properties which have been sold without our knowledge. please advice