Complex sentence: While in the third district, players, even if they're from opposing factions, cannot harm each other no matter what, the other 2 districts allow players from opposing factions to attack each other during certain mission scenarios.
Split into simpler sentences: While in the third district players, even if they're from opposing factions, cannot harm each other no matter what. In the other 2 districts players are allowed to attack each other (so long as they are from opposing factions) during certain mission scenarios.