Hi @jonathanmerrill,
I think we need a little information before we can help you, so I have a question and then some options to consider.
Are your fellow colleagues faculty at your institution or are they "guests" that are not faculty at your institution?
If your fellow colleagues are faculty at your institution, you might need to ask your Canvas admins to either (a) create a Canvas user account for them or (b) add them to the course for you because you might not have permission to.
If your fellow colleagues are not faculty at your institution, I would recommend that you contact your Canvas admins to find out if your institution allows "guest" user accounts. If they allow "guest" user accounts, if student privacy is a concern (and it should be), you could work together in a sandbox or development course (the name used can vary by institution) instead of a course where students will be.
If using a sandbox/development course, when finished, you could import the content/design into your own course and your fellow colleagues could export the course out of your institution's Canvas environment and import it into their own environment.
I hope you found that information helpful.
-Doug