OK, so you added the regions in your information file and printed them on your page template, that's fine. First, delete your
region--footer.html.twig again. Then, in the back-end of your site, go to Structure> Blocks. The newly added regions should appear there. Now place some blocks in your newly added regions. Save, empty the cache and visit its interface again. Your regions should be populated now.
And with respect to
region--YOURREGION.html.twig templates that you should have already deleted, these will only be collected when these regions are populated, with blocks. Otherwise, these regions simply will not print at all.