Importance of signature in registering property & procedure (MUSLIM)

My grandpa has 6 children and my dad bought the property of my grandfather after he expired. Per my grandpa's will, 1 share is for girl children and 2 shares are for male children. My dad settled the amount to 4 of his siblings and registration (release deed) was done during the year 2002. My dad's elder brother was settled in abroad and he s unable to come for registration. but it was mentioned in the registration document that so and so amount is pending to the person due to him staying in abroad and we have to settle it to him once he comes india. Later, in 2016, my dad transfered the property (his 5 shares excluding his brother's share) to my mother's name. registration was done for 4 cents without including my uncle's land. Now, when we approached for loan, they are saying the document is invalid as my dad's brother has no signed it. How a document can be registered without all necessary signatures? How we re-registered it to my mother's name? Chitta, EC issued n my mother's name