I used Backroller Classics on my front rack. My rack had higher mounting points, so maybe those won't work for you, but it worked great for me. With a touring bike and most of the rider weight on the rear, and most of the gear weight on the front, it felt fine, a very solid ride.

I will say, though, that I always had a rear rack, so even though the bulk of my gear was on the front, I could strap all manner of things to the rear rack if I needed them. But you also have the advantage of two people. I found that one pannier was completely devoted to sleeping: tent plus insulation. The other pannier had clothes, cooking gear, tools, etc. With two people and four panniers and an assumption that you'll only need one tent and one set of cooking supplies, you might have an easier time getting everything in. If not, there are options to carry a little more that don't involve a rear rack: Saddle bag, frame bag, top tube bag, handlebar bag. I use fork-mounted, Anything Cages, but I use those instead of a front rack now, not in addition to a front rack. But sometimes I mount one cage in my frame triangle when I'm not using a frame bag, which gives me another option on where to stash a few things. My nested cookset/stove fits nicely in an Anything Cage.

So I'd be inclined to set out your gear and see what you can do without, and what you can fit in. Maybe allocate two panniers for communal items like tents and cooking, and one pannier each for personal items. If that leaves you still hurting for space, there should be other ways to carry a little more without adding a rear rack and another set of panniers.