What is the ruling on praying in a mosque located among a group of graves and a dome, which is visited during celebrations, and whose key is given to those who believe in the graves by the imam of the mosque or the caretaker?

Islam has warned against taking graves as mosques and building over them or incorporating them into mosques. However, if the graves are outside the mosque and there is a separator between them and the mosque, then prayer in the mosque is valid. Elevated graves and domes built over them must be demolished when possible and if there is no fear of discord, based on the Prophet's (peace and blessings be upon him) saying to Ali: "Do not leave any image but you efface it, nor any elevated grave but you level it."