Is there evidence for the order of placing several bodies in one grave according to scholarship or Quran memorisation?

Summary

Guidance exists in the hadith of the Prophet and in the explanations of jurists that the body with more Quran memorisation is placed first. By default each body is buried in its own grave, and burying more than one together is permitted only out of need or hardship, such as after a battle. Stated conditions include separating by gender unless related as mahram or spouses, placing a barrier between bodies, and not reopening an old grave unless the earlier body has decayed. Imam al-Rafiʻi also mentions giving precedence to a father over a son and a mother over a daughter.

Written in our own words from the original fatwa — check the source before acting on it.