Finally finished this with my pathetic non-raid box group. My group is a bard, chanter, and druid plus mercs (tank, caster, and healer). While I don't yet have all of the new merc AAs for the classes, I have a lot of them, and I invested in all of the new merc gear (yup, bought it from the bazaar). The first 15 mobs were easy enough. It was the final 4 mobs that killed part/all of my group on attempt after attempt.
What was most helpful is that if you are invis, the final 4 mobs are indifferent, so you can place your group where you want them before engaging the mobs. There is just enough time between the death of the last of the 15 mobs and the entry of the 4 linked mobs to cast 1 or 2 buffs, then invis up the group. The mobs will line up facing where you zoned in. I put the chanter to the side of the mobs and mez'd them from there. The chanter mez is like a rectangle - side to side is more narrow than front to back.
If you run into trouble, you can exodus with the druid, and that brings you to the next big island over, along with erasing agro. If any char died, you can invis up to run over and drag the body back to the safe island. You can rez and rebuff there, then invis up, go back, and try again. After trying all of the various root and mez spells and AAs from the druid, chanter, and bard, I finally succeeded by sitting right next to all of the mobs, spamming Perplexing Wave (rank 2), and picking off the mobs one by one. As needed, I succored/exodused the group out, which was pretty much after each kill of the first 3 mobs. Djinn were more resistant to the mez than armor guys, so I killed the djinn first.