Hiya @calibre and sorry to be so slow to respond to you!
Our intention and hope is that if you’re collaborating, the account owner invites their collaborator to the netlify team (see Manage team members | Netlify Docs for details), and they have separate logins but work together on the site(s). Our Support team can help transfer ownership of a Starter team to a teammate (or a totally new owner); you can ask here and we’ll get back to you much faster than 11 days hence for a query like that one! :))
On a Pro or higher team, you can have multiple owner-level members, each of which can invite more owners or remove old ones who have moved on.