What is the ruling regarding land whose owners discovered, during excavation, that it was a cemetery without any markers and not very extensive, and they continued construction after moving the bones they encountered? Are they sinful, and what is required of them?

The default is that it is not permissible to exhume a grave due to violating the sanctity of the deceased, but scholars have permitted it in two cases: necessity, or if no trace of the deceased remains. Since the aforementioned act has been carried out and does not fall under these two cases, the perpetrator must repent to Allah, return the bones of the deceased to their places, and not build on the said location.