So yes this is long winded. I may break down and make standalone videos as well. This is more about the math and how it works rather than just giving the solution. Got the numbers in the description if you don't want to watch or timestamps where I show how it is done.
2x2 grid 1080p resolution:
Set video Zoom to .5
Positioning of each video:
Video 1 X -480 Y +270
Video 2 X +480 Y +270
Video 3 X -480 Y -270
Video 4 X +480 Y -270
2x2 grid 4K resolution:
Set video Zoom to .5
Positioning of each video:
Video 1 X -960 Y +540
Video 2 X +960 Y +540
Video 3 X -960 Y -540
Video 4 X +960 Y -540
4x4 grid 4K resolution:
Set video Zoom to .25
Video 1 X -1440 Y +810
Video 2 X -480 Y +810
Video 3 X +480 Y +810
Video 4 X +1440 Y +810
Video 5 X -1440 Y +270
Video 6 X -480 Y +270
Video 7 X +480 Y +270
Video 8 X +1440 Y +270
Video 9 X -1440 Y -270
Video 10 X -480 Y -270
Video 11 X +480 Y -270
Video 12 X +1440 Y -270
Video 13 X -1440 Y -810
Video 14 X -480 Y -810
Video 15 X +480 Y -810
Video 16 X +1440 Y +810
0:00 Intro
0:35 Explaining how the process works
12:13 2x2 grid at 1080p resolution
14:47 2x2 grid at 4K resolution
16:42 4x4 grid at 4K resolution
23:14 4x4 grid at 4K resolution alternatives