Hi Ben,

Unfortunately, there is not currently a way to add co-teachers to a class. This is a feature request that I have seen from several other users, and I've already alerted the development team of its popularity. 

As of right now, I don't know of any plans to add this feature in the near future, but I'll let you know if I hear anything else.

Let me know if you have any further questions!

Looking forward for this feature to be added! -Samuel

Is this still not an option?