I would suggest we reduce the lethality of the battle by using leather armour and wood or stone swords.
Or we could do it my favourite way.
Give a kit to each team. Each team of 7/5 Would have 2 bows, 2 iron sword, 3 stone swords, 1 wooden sword, 2 set of leather, 1 set of iron, 64 arrows.
That way each team would have to organize and plan who gets what. Someone who is the best pvper would have to choose leading the attack, so he would need the iron set, or being in the back as their secret weapon.
What do you think of having kits? If possible, keep the supplies extremely limited, its only fun when there's a limit, not to see everyone in the same armour, same equipment, that would be boring...