Yosef Karo

“ One who puts his deceased in a coffin but does not bury him in the ground, transgresses [a negative commandment] of not letting a dead body sit overnight. And if he put the deceased in a coffin and buried him in the ground, he does not transgress the commandment. Nevertheless it is best to bury the deceased in the ground itself, even outside of the land of Israel. ”

“ We do not bury a wicked person next to a righteous person, [and we do not] even [bury] a seriously wicked person next to a slightly wicked person. And similarly we do not bury a righteous or upstanding or average individual next to an outstandingly pious person. Rema: But we do bury a baal tshuvah next to someone who was a fully [i.e. for one’s entire life] righteous person
Seif 6: Two people who hated each other, one should not bury them together. ”