Sometimes you need to keep two upstreams in sync with eachother. For example, you might need to both push to your testing environment and your GitHub repo at the same time. In order to do this simultaneously in one git command, here's a little trick to add multiple push URLs to a single remote.
Once you have a remote set up for one of your upstreams, run these commands with:
git remote set-url --add --push [remote] [original repo URL]
git remote set-url --add --push [remote] [second repo URL]
Once set up,
git remote -v should show two (push) URLs and one (fetch) URL. Something like this: