Both sides are in character and have no qualms with going for the kill. Escanor and Merlin are excluded, as we've seen very little of their fighting ability. This is Meruem after his fight with Netero (minus the poison) and we're assuming that he has all of Pouf's and Youpi's powers. The fight is won by the death, or inability to continue fighting, of everyone on the opposing team.
None of the sins have their Sacred Treasures (except King). They fight him one at a time, in the order of Gowther, (fairy) King, Diane, Ban and Meliodas. Meruem has no rest in between.
Gowther, (fairy) King and Diane have their Sacred Treasures. They fight in the same way and order as above.
None of the sins have their sacred treasures (except King). They fight Meruem all at once. Ban is not allowed to steal Meruem's power (strength, speed, etc.)
All of the sins (except Ban and Meliodas) have their sacred treasures. They fight Meruem all at once. Ban is not allowed to steal Meruem's power (strength, speed, etc.)