The ruling on exhuming the remains of the dead who were buried in a single grave

Question:
A man had agricultural land. One of his sons passed away, and he buried him in this land. Then, after a period of time, another son passed away, and he placed him with his brother in this grave. After another period, he moved his wife’s bones and placed them in the same grave, as it was decided that a public road would be built over her grave. Thus, this grave came to contain three people. After this man passed away and his sons grew up, they wanted to build on this land, but the grave was in the middle of the land, causing them difficulty. The question is: Is it possible to move the remaining bones from this grave to the Muslim cemeteries, so that they can benefit from this land?

Answer:
It was a mistake to bury them all in this land. This is an error. In fact, it is obligatory that each person be buried in a separate grave, provided one is able to do so, and that they be in the Muslim cemeteries, not in their land, not in their house, and not in their courtyard. It is obligatory that they be with the Muslims in the Muslim cemeteries.
Therefore, the existing sons must move the bones to the public cemetery. Each set of bones should be in a grave that is alone in its own pit, and its surface should be leveled like a grave, so that it is respected like the other graves, not trampled upon or desecrated. They should make every effort to separate the bones of the first person alone, the bones of the second person alone, and the bones of the third person alone, with each one in its own pit. Then, they should level the surface like the surface of the graves in the Muslim cemeteries, the cemetery around them. There is no harm in their using the land.