What is the ruling on the children of the deceased exhuming their father's grave 25 years after his death to bury their mother in it, claiming there is no space in the cemetery, even though there is another cemetery, but it is far away?

It is not permissible to exhume a grave and bury someone else in it unless it is confirmed that the first deceased has decomposed and nothing remains of their flesh or bones. If anything remains, the prohibition persists. However, if it has decomposed and turned into dust, then it is permissible to bury in its place. This varies depending on the country and the land, and the opinion of those experienced in the matter should be relied upon.