Can xerox copy of mutual agreement be permission in court?

My grandfather and his brother had land side by side. The land closer to road is with his brother, and land farther from road assigned to my grandfather. My grandfather has a mutual agreement on the land that connects the main road and interior land such that land will be a common way/passage to house built in interior land, in 1980s. We have xerox copy with signatures of grandfather and his brother, along with 4 witnesses. Now, we started building our house in interior land. But the son of grandfather's brother, is asking us that he will not let us to go to our house from that common way/passage and, claims that land belongs to his father. He says that he has land ownership document of his father. Now he warns us that he will put case on us and he won't allow us to go through the passage, which we are using since 1980s. If he files a case for that, can that xerox copy of agreement with all witnesses be permissible in court that grandfather & brother have agreement that all of us will have access to that passage/way? Please help.