Is it permissible to lower a deceased male onto a deceased female in the grave, and what is the permitted time interval between lowering the two deceased?

It is not permissible to bury more than one deceased person in a single grave except in cases of extreme necessity, such as limited space or difficulty in digging. An exception to this is what the Companions did at [the Battle of] Uhud, where the Prophet permitted the burial of two or three individuals in one grave due to necessity. When burying more than one person out of necessity, a separation should be made between men and women using an earthen barrier. The man should be placed first, then the boy, then the woman. Burial in fasaqi [multi-person tombs/vaults] is disliked as it contravenes the Sunnah (definition), especially regarding the mixing of men and women without a barrier. Furthermore, it is forbidden to exhume a grave to bury another person with the first unless the first deceased has completely decomposed.