How to claim my benifits on the property of my husband?

I’m an Indian woman who got married to a foreigner, who settled here in India before 10 years with PIO card issued from Indian government. My husband got married in his country and got divorced legally before he come to India and marry me, but he have three children who born for him and his first married wife who all are residing in his country. After we got married here in India legally, we have a son who born for me and him, and then we purchased a property (house) here in India on his(my husband) name after getting all necessary approvals from Indian government, RBI. Now, my husband or our lawyer failed to write a separate will towards me on this property (house where we residing now) because he got sudden heart attack and passed away a year ago. My question is, now how can I get legal rights over this property in India and also kindly advice the rights me and my son have on this property. Note: I have all original documents with me and same i mentioning below, *All property documents of this house in India. *Proof towards the pension which I receiving from his country to my bank account. *My husband first marriage divorce certificate *Government approval towards my husband to live in India (PIO Card which is valid still) *Our marriage certificate *Passport of Mine with his name as husband *My son birth certificate *My husband death certificate issued by Indian government *(i can get a proof from church for all other stuffs i done after his death (e.g.: grave, bill etc.,) ) Thanks in advance.