GPA Process in case property in Bnagalore and Seller in Hyderabad

Hi, I am planning to buy a flat in Bangalore. The seller lives in Hyderabad. Property is in name of Mother and Father (jointly) of seller. His father got expired in 2016. After that, they visited BBMP office in Bangalore and did some transfer, but in EC obtained online, I don't see this transfer. EC still shows property in name of seller's mother and father jointly. Seller has one sister as well. As per my local advocate, he has to bring GPA from his mother and sister to complete the deal. Seller's advocate is suggesting him that his sister's GPA is not needed. Also, as per seller's advocate, if seller goes for GPA in Hyderabad, seller has to pay 5% of property value. Seller is ok with GPA but he is not ok with 5% stamp duty for GPA. I searched on net, and it seems 5% stamp duty is not valid in case of close family members and only 1000/- stamp paper is needed + some changes for registration of GPA. Please guide me if my understanding above is ok? Do you see any other document/loophole here?