Bike carriers are like tents. A four person tent will hole four people, but only three comfortably. We have carried four bikes (of mixed styles) on a four bike Thule Apex (or a model that looks a lot like it). It takes some creative packing to get all four of them on, though.; this saddle over that bar, that bar through this wheel kind of thing.
A couple of suggestions. First, bungee things down -- you don't want Bob's front wheel swinging back and forth and the handlebars beating up Susie's bike. Second, if you're carrying mixte (girl's) bikes, look for something like the following. It gives you a "level" mount point for a hanging rack, and attaches under the chainstay and stem.
Yakima TubeTop Frame Adapter [8002531] | Accessories - Performance Bicycle (performancebike.com)