I Need Help On Xenosaga

Well, a week ago I got a new PS2 since mine was broken and would cost more money to fix than to buy a new one. So anyways, I picked up Xenosaga because I heard it was great. I am now stuck at a certain boss. I am inside a gigantic gnosis, and am at the core,(around 12 hours and 30 minutes into the game) where I am at the Zohar and this gigantic Gargoyle and his two buddies (can't remember name, they look like slugs floating in the air) attack me. I don't know how to beat them because they deal ~200 damage a turn to my people through 2x Hell Rise or something. I was just wondering if there was a tip to beat them, because the Gargoyle regenerates his HP and it's deathly hard to beat the other two. Any advice?