Yes, you can import the clips into iMovie from each of your four cameras, either by importing them into a time line of a project or into events that will displayed in the iMovie media sidebar from where you can access the clips for various projects. You can then edit them in any of a number of ways, such as by trimming them, moving them around the timeline, inserting them into another clip with the Picture in Picture feature, displaying clips side by side with the Split Screen effect, or using Cutaways to switch back and forth between clips.
-- Rich