In Premiere Pro I would most likely do crops on each video using Crop Effect.
I would crop them to a design / composition that I would establish in the Titler. eg the frame bars created from Lines of appropriate width.
This Title I would use as both an overlay to adjust crops to as well as the frame bars eventually.
You will need 5 layers of Video and the Title above all of them for your example. Easily done in PPro.
I haven't used elements in 6-7years so apologies if I miss the mark.
Am assuming videomerge merges the layers down to simplify timeline (akin to nesting?! in Pr) as haven't come across this before. Either way you probs shouldn't need to do so - put each video in a separate layer and crop and move as you have done and render and should come out great as one video file (no need to then video merge).
If you do insist on video merge, move the central big size video to the bottom layer with the 4 small ones to layers above. Then when you merge down the side videos won't get obscurred
Or use garbage matts - look in effects and should be there. Drag and drop on each clip and move cornersto selct area you want to keep just as you would for a crop. See if that sorts your problem out.
Re Premiere Pro. Great piece of software but more complicated so might not suit your needs (though may do) but not cheap (even with edu discount) if not using it for your job (check creative cloud subscription cost). Worth checking out DaVinci Resolve 11 if you want pro software (which is now free as a result of buyout)- mostly for colouring but also has editor. If you do start making decent money on Youtube (though for all I know you could be! :-) ) and want to get into some complex editing and feel limited by Elements, then definitely get pro - you won't regret it at that stage in your editing.
Finally, your screenshots genuinely look very impressive, I like the split view and nice to see people pay attention to lighting - I think lighting and sound are just soooo important (more so than what camera and lens) and far too often overlooked.
Just occured to me about render order of effects. Don't know if elements gives you effects tree/layers allowing you to move effect up or down in order, but if so, moving the merge effect below the crop effect may sort issue out.
Premiere renders the bottom layer first then renders the layer above it and superimposes it and then renders the layer above and superimposes it on top and so on. For effects, Premiere renders within each layer from the top down.
Thank you so much for the quick reply! I think you might be onto something there. I just shut off my laptop but tomorrow I will try to move the videomerge effect below the crop effect and see what happens. I will keep you updated on if it works!
I am also glad you like my screenshots. Natural lighting is my best friend haha.
Glad it works :-)