You need to store players who hit the rb in a collection, then on death you will broadcast to every player that did damage the rb the html message
if (attacker instanceof L2PcInstance) {
L2PcInstance player = (L2PcInstance) attacker;
if (!_damageMap.containsKey(player.getObjectId()))
_damageMap.put(player.getObjectId(), damage);
else
_damageMap.put(player.getObjectId(), _damageMap.get(player.getObjectId()) + damage);
}
should be something like this