Procedure to get DNA test order from the court for share in property

we are hindus. My father died in 1980. my father had married my mother without divorcing his first wife. there is no proof abt their marriage. my father left behind land and other properties in the village where his first wife and my step brothers reside. now recently when we filed for partition suit, they replied in court that their father never married twice and they dont know us. So how will i prove that we are our fathers children.i have legal documents such as school leaving, passport, domicile certificate, birth certificate all has my fathers& grandfathers name on it.we have 2-3 old photos of me and my father. besides this we have no other documentary proof. Is the above proof enough to prove that i m my fathers son? although our other relatives know us they dont want to interfer and dont want to be witness in court. what other proof will the court require? Can the court order dna test with my step brothers that we have the same father? Thanks