Property distribution

Hi Sir,

My grandmother has owned property(4 acres land). She has 2 daughters(elder) and one son(younger). The younger son is my father. We are ruling the my  grandmother land. Now the two daughters are asking the share from my grand mother property. But All the properties are earned by my grandfather's, not an ancestor property. If they apply for the share via court. will it be valid for them? 

Please suggest me?