Last time I had to make a video for multiple screens I created the full in AE and then created individual comps for each part, I precomposed the full into those individual comps. Then I made another comp that put all of those subcomps back together to make the full size again to check that they were going to export the correct areas.
Then I exported the individual comps. You could do the same thing in premiere.
Another way to do it would be to just set crops in media encoder. It all depends on how long it takes you to export and how you want to see it.