@Marianne_Mikalsen The best solution I can think of is pretty manual and doesn't leverage any special Teams functionality, but would keep your document security intact and let your team operate from a single document version.
Assuming your site collection has external sharing enabled, I'd recommend creating an access link for "specific people." My assumption is that one link is created, and that one link serves as a single access point for however many people you invite at that moment. If any external collaborators get added, you'd need to make the link again, as you're counting on having one link available for all of your external collaborators to use. With that link, post it somewhere easily accessible in Teams (maybe a Wiki) and that's that.
