How to get a share if property is transferred by misguiding

Hello My Father are 6 brothers, my late grandpa had transferred his property in 6 equal parts among them. My younger grandpa who is not married had also transferred his property among my father and his 3 brothers. 2 were not given the share of his property as my younger grandpa was ill treated by them. But as a brotherhood my father and other 3 convince my younger grandpa to share the property among all six. So on a decided day they met and signed the document to transfer excess part of property from three to other two, till then one of my uncle expired and because of that, his children and wife didn't agreed to transfer there share of property. Now recently we came to know that those papers which were signed were not of our younger grandpa but was of our late grandpa. Now I want your advice how can we get that share, which was ours and my 2 uncle transferred them to themselves by getting sign on wrong documents. And they have a loan on that property too. Religion Hindu