If your sibling is refusing to share your late mother's property documents, including the death certificate, and is unwilling to share the property itself, you have legal recourse. You can attempt to gather property details through relatives or by obtaining an Encumbrance Certificate (EC) from the Sub-Registrar's office. If direct requests fail, you may need to file a suit for partition to claim your share of the inheritance. Consulting a local lawyer experienced in inheritance law, particularly under the Dayabhaga school applicable in West Bengal, is highly recommended to navigate the legal process effectively.