simplest with hstack (1)

Watch on youtube.com

doc

https://ffmpeg.org/ffmpeg-filters.html#hstack, https://ffmpeg.org/ffmpeg-filters.html#amerge, https://ffmpeg.org/ffmpeg-filters.html#pan

It is the simplest approach and it will be usable if you do not mind not having an aspect ratio maintained.

#! /bin/sh
pref="`basename $0 .sh`"
vleft="EuropeanArchive.mp4"
vright="Eduardo.mp4"

#
ffmpeg -y -i "${vleft}" -i "${vright}" -filter_complex "
[0:v]scale=960:1080,setsar=1[0v];
[1:v]scale=960:1080,setsar=1[1v];
[0v][1v]hstack[v];

[0:a][1:a]amerge=inputs=2,pan=stereo|c0<c0+c1|c1<c2+c3[a]
" -map '[v]' -map '[a]' \
  "${pref}.mp4"