Maybe (And I say maybe, because your code is a mess), but you should go at L2PcInstance and find the method updatePvPStatus
public void updatePvPStatus(L2Character target)
And add your zone there. For example:
(It is better if you move your zone with the others zones package).
@@ -4190,6 +4190,9 @@
if (isInDuel() && player.getDuelId() == getDuelId())
return;
+
+ if ((isInsideZone(ZoneId.FLAG) && target.isInsideZone(ZoneId.FLAG)))
+ return;
+