Not all of the Op 4 Hives have been released yet. We have three more to come - The Gatekeepers; The Split; and The Mist (I think in this order as well).
PC players can change the date on their PCs to access these unreleased Hives, and console players can play them if they join a PC host who has done this (I’m a console player and I’ve played these future Hives myself but not mastered them yet).
One of the guys on the forums has mastered all of these Hives (as well as past Hives) solo using Cole, but this is more of a reflection of their ability more than anything!
With The Malfunction, I’d say Cole isn’t even needed. Fahz is more useful on this Hive in my opinion. The other two characters can vary and I’ve done it with several combinations like Mac, Keegan, Clayton, Cole, Kait, Lizzie…
The Ambush, I found Cole useful as the rear guard to deal with the Juvie spawns, but this is on account of him being very tanky. Having said that I’ve done this with different characters in this role too. This Hive is easy if you have a designated rear guard. It’s a boring job, but a very important one. This Hive becomes unnecessarily hard if no-one watches the rear and you get Juvies all over you. Again I found that Fahz is very good for leading the way and sniping everything (especially if you get the Sniper spawns - but nonetheless you get a Longshot halfway through the 1st section). Keegan is a good choice as well as there’s a Boomshot early on, but again, this Hive I’ve done many times with lots of different combinations of characters.
The Onslaught - now this one on the surface is very tough. The first half is straightforward, but the second section is very tough due to the sheer numbers of enemies it throws at you. However some players are aware of a way to exploit the spawns and you can basically run through the second section (but at the expense of a strong score). The first half can be easily done using your core basic skills and using the turrets. The second half, if you run I’d suggest at least one team mate go as a tanky character like Cole, COG Gear or Clayton just in case as you’ll be running past several Elite Drones.