L2J Server

I've been testing the Infinity Twin following some reports of the players on my server and the truth is always become invulnerable.

I tried all, tried to kill both being within the circle where they appear but I always turn invulnerable.

Twins are still poorly implemented or is there some mystical technique to kill them?

Once they get invulnerable, its almost impossible to make them vulnerable again

I note that this raids have a toggle "Ultimate Shield"
If i remove the toggle with GM then they are vulnerable again.

It is correct that this raid have this toggle?