1. Registration of WILL is not compulsory. Even an unregistered WILL is legally valid if it is signed by 2 witnesses and the Testator was of sound mind and there was no threat of force, threat, coercion, etc., in bequeathing the property to anyone of his choice.
2. Since the WILL is executed more than 30 years ago, it's barred by limitation. It's difficult to challenge the WILL after the lapse of 30 years.
3. You should secure the original WILL of person "A", his death certificate, deed of his self acquired property, his family tree, khata certificate, sale deed of the property in favour of "C", etc.
4. Please refer to answer in Sl.No.2.
5. Please get the property papers verified by a Lawyer and obtain his opinion before proceeding.
6. As per your narration, "A" had self acquired this property and being an absolute owner of the self acquired property, "A" was within his legal rights to have bequeathed his self acquired properties to only his sons and none to his daughters.
7. In 2006, "B" sold the property even though he had minor children, since it's not ancestral property, the children of "B" did not have right over their father's self acquired property during the lifetime of "B", it's in order.