legal wife ' child and illegal wife ' child rights

Gd mrng sir..i have so many problems from childhood..my dad got second marriage in 2005 with divorce. But my mother filed a case against divorce..court has cancelled his divorce with my mum.he had two child (girls) with second wife.we are two one boy and one girl.now we want to do the marriage of my sister.but my dad not going to do this..how can i solve this problem.my dad is a govt employee..and how can i get his propertys..? Can we get whole property ? Courte has alredy cancelled his divorse..now second wife is illegal or not ? Plzz plzz solve this problem