Unknown property of a person

Hi there I am just curious about this and I believe it’s very common and it happened before. My grandfather was well settled and he had a lot of properties as far as we aware. When he passed away 13 years ago in hospital , 2 of my aunties didn’t even come to the hospital first instead they went to our home & took all the legal documents from his locker. So none of my other uncles including my dad knew anything about properties my grandfather owned/transferred to my Father & uncles. We know this happened and when we confronted our 2 aunties they said there was only 2 documents which is the home my grandfather lived and his shop.. they also said there were no other documents, which is too good to be true.. So my question is: 1.) is there any way to find out if there were other properties documents registered in my Grandfather name or my uncles names? 2. If yes, my aunties are just waiting for right opportunity to transfer the properties into their names. If they do or did so, is it valid ? 3. If they haven’t transferred to their name yet but yet they are using the properties to generate income all these years. Can we get them to hand over the original documents to us and what do we do if they refuse to handover ? Thanks a lot in advance