To list all remotes
git remote -v
To rename remotes
git remote rename oldname newname
To push all branches to all remotes:
git remote | xargs -L1 git push --all
Or if you want to push a specific branch to all remotes: Replace master with the branch you want to push.
git remote | xargs -L1 -I R git push R master
(Bonus) To make a git alias for the command:
git config --global alias.pushall '!git remote | xargs -L1 git push --all'
Running git pushall will now push all branches to all remotes.