Idea:
- download the videos to your computer with yt-dlp
- Open up 4 videos at once with a local video player app that opens videos individually by window 3a. Resize each window into quadrants for the monitor 3b. Get four monitors and stack them in quadrants 4 success!
MPV/SMTube has a yt-dlp plugin that works but needs to be recent versions of both player and yt-dlp to work right.