Hi Molly,
No worries! I think you're right about the relationship class. I considered this, but also has its drawbacks from a user-interaction standpoint.
This is definitely something my team is still struggling with in multiple maps, but I have heard rumblings of future Field Maps enhancements that may help in this space, and make it easier to calculate form attributes on the fly! Watching closely...
Thanks,
Larissa 🙂