Is it permissible to bury males and females in a single grave?

There is a scholarly consensus on the impermissibility of burying more than one individual in a single grave, unless [absolutely] necessary, as when there is insufficient space [in the graveyard], the absence of someone capable of digging a grave, or when another grave is not available. The Messenger of God (peace and blessings be upon him) and his Companions were accustomed to burying each individual separately except out of a necessity.

When a necessity exists, the most meritorious is buried first facing the qibla (direction of prayer) followed by the next in the degree of merit and according to the order of preference concerning the imamate (leading others in prayer). This is because of the hadith narrated by Jabir who said, "We complained to the Messenger of God on the day of Uhud and said, 'O Messenger of God! It is a hardship upon us to dig a grave for every [dead] person!' So the Messenger of God (peace and blessings be upon him) said, "Dig deep, dig well, and bury two or three persons in a single grave." They said, 'O Messenger of God! Whom should we bury first?' He replied, "Bury the one who memorized the Quran the most." Jabir said, 'My father was the third of three to be buried in the same grave’" (reported by al-Bukhari and others).

A wall of earth should be made as a barrier between two individuals buried in the same grave. A father should be buried before (physically in front of) his son out of respect, even if the son were more meritorious. A mother should be buried before her daughter. Women must not be buried in the same grave with men, unless when absolutely necessity, and on the condition of putting a barrier of earth between them. A male should be buried before a female, even if he were her son, and a male is placed at the head of the grave and the female at the foot.

And God Almighty knows best.