I designed a custom event for the L2jMobius Interlude chronic. However, despite trying everything within the script, friendly fire is still active, and friendly units within the same party can attack each other during the event.
After checking the pre-configured CtF (Capture the Flag) event, I noticed that friendly units are also able to damage each other there as well. I believe this is a bug in the core/source that needs to be fixed.