All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
It is forbidden to exhume a grave, except for a necessity, to preserve the sanctity of the deceased. An example on this necessity is that the deceased is buried in a usurped land and its owner asks for moving his/her body to another place. In this case, the grave must be exhumed, even if the deceased has decomposed, to give rights to whom they belong. However, it is preferred that the owner leaves the deceased there to preserve his/her sanctity.
According to your (Asker`s) question, the deceased was buried in a land owned by another family; therefore, if the owners of that land insisted on moving the body, then it is permissible to be moved. However, we advise the asker to bring the owners of that land where his father is buried and have them write down their request and then it will be approved. And Allah The Almighty Knows Best.