Ancestors property issue.

Hi, my grandfather has property a shed of 300sq yards. At that time we have given permit to small room to younger brother for his daily living. After demise of my grandfather, we 3 brothers mutually divided the shed into three parts 100sq yards each. It was written on plain white paper duly signed by all 3 of us and other witnesses too. He built his house in his place of 100yards and shifted his current meter box from small room to his newly built house. But the house number of the total shed remain the same. He continued to pay his house tax for his 100yards home. This was continued for more than 25 yrs. Leaving the empty partitioned place of other two brothers. Recently at the time of new surveyor he said the whole area was his own as he showed the house number is same for his house and the total house area. Now he claimed the whole property as a unknown plot/ land and paying the tax and living there for more than 25 yrs and physically adverse possession of the property. Now he is not allowing us. My grandfather assets was on a stamp paper. This is the only document I have where we can show that he purchased from someone. Earlier days there was no EC or online records. And a paper duly signed and witnessed by people. Can I file a case of cheating on my brother. Or how can I get my share which is still a open place and my brother not allowing me there as he made registration and gifted on name of his wife. Please help.