Are you willing to lose the top and bottom of your video in order for your video to fill your 16:9 frame?
Also note that, if you do decide to stretch out your video so that it fills a 16:9 frame, you'll be losing resolution, since your video will have to be a third larger than your original footage, which will mean your video will look softer and kind of blurry.
Is it worth that to fill a 16:9 frame?
There are a number of challenges to doing this, including the fact that doing so will require lots of rendering and the even bigger fact that, if you're planning to show this on a TV, up to 10% of the edge gets cut off, which means that any text you've got outside of the "safe zone" might be off the screen.
But, with those caveats, place the upper left corner video on Video 1, select it and open Applied Effects. Open Motion and set the Position and Scale so that your video sits in the upper right corner.
Add your images to Video 2 and do the same thing, setting Position and Scale so that it is in the lower left of your screen. Then add you main video to Video 3 and set its Position and Scale so that it is in the right 2/3 of your video frame.
As I say, there are a number of potential problems with this kind of composite, so I'd recommend you do a very short test composition first, then output it and show it on the device or web site you hope to display it. That way you'll get the bugs out before you go investing a week's work into something that has you scrambling to fix at the last minute.