You've discovered a registered sale deed from 1963 for a property now in possession of the seller's heirs, who claim ownership through long-standing possession. The original buyer and seller are deceased. Legal advice suggests taking court action to claim possession, as the seller's heirs cannot claim adverse possession over property they sold. It's crucial to consult a local property law expert with all your documentation to understand the best legal strategy, including potential claims for possession, declaration, and injunction.