How do I get the 4v4 insane AI kin achievement?

OK, so the AI seems to be updated.

AI will now react if you build buildings close to it. You can still rush the AI, but the builds have to built at much larger distance.

Zerg is specific, there is a pathing bug. When you build the spine crawler in a gap between minerals in the mineral line, all the drones will try to assault it through the gap resulting in only one drone attacking at a time. I suspect that this will be patched as well.

When fighting four zerg i found out that a good strategy was to go with 3 terran allies and as terran mass siege tanks and marines. Use the Megaton map and siege up in the center. It is very important to have some siege tanks ASAP in order to be able to wipe out the first attack. Then place your tanks at the cliffs/center and wipe the second attack. After that you need to severely cripple/destroy at least one of them, prefferably two. I used vikings for vision and sieged their main bases close to the middle. If this fails, you will probably lose since they will tech up and roll over you.

There are probably better strategies, but this one worked for me (after a few tries and a bit of luck). The reason is probably that insane AIs are very aggresive and as Zerg, they mass lings, hydras and roaches in the beginnig. Siege Tanks counter this well. Do not worry about a different strategy in the beginning, since your allies will mass infantry and the enemy will counter this with hydras, lings and roaches.