Find line (Even if true):

<property name="FriendlyFire"	value="false" />	<!-- Can friendly players damage each other (PvP) -->

delete it and replace with:

<property name="PlayerKillingMode"	value="3" />	<!-- Player Killing Settings (0 = No Killing, 1 = Kill Allies Only, 2 = Kill Strangers Only, 3 = Kill Everyone) -->