Hey PBK,
I would suggest starting by creating a shared "slimmed down" Google account (not tied to Gmail, Google+, or any other Google service) for the company email address
here. Use that Google account to log into Firebase.com and make it the owner of all of your Firebase apps. Use some mechanism to share that password with your entire team, or only those who need it.
You can then add personal Firebase accounts as collaborators from
your account dashboard. Collaborators can do everything an owner can except managing members, managing billing, and deleting the Firebase app. Collaborators do have admin access to the Firebase app dashboards though which is probably what you want.
We do this internally and it works smoothly for us. It is a bit of a pain to share a common password for our shared account, but this will be getting better in the future.
Another option you can do is just have one person be the owner of your apps and have them control billing, app creation / deletion, and managing collaborators. Adding other team members as collaborators will grant them enough admin access to administer the apps otherwise.
Cheers,
Jacob