Acquiring legal heir certificate for legally wedded second wife & her children

My father passed away on 12-Jun-2015. He was a divorcee and he re-married my mother by traditional Hindu wedding. He had no children from his first marriage. He has an unregistered will which details how the assets should be split amongst us siblings. We applied for a legal heir certificate amidst the pandemic through online portal. Our application was rejected on the grounds that divorce papers hasn't been furnished and also stated that the second marriage is void unless it is registered. We have photographs of the wedding, relatives to vouch for the marriage, NPR receipts, voter ID and other govt issued documents to establish their relationship. Moreover, they have had lived in their own house for over two decades. I was shocked to hear that their marriage is unrecognised from the purview of the law. I would like to know how to proceed forward. PS: It's an open secret that the revenue officer is corrupt and she extracts money from applicants even if application is completely in order. Let me know what to do if she attempts to stall the application again.