Recommendations for MongoDB Driver and Schema solutions?

What is the best solution to implement the two APIs side by side. Use the Atlas/Realm for some data fetching and the Prisma/Redwood API for some.

This part I’m still unclear on; what exactly do you want/need the Prisma/Redwood API to do? If you are doing the whole authentication flow with Realm as well and the data is stored behind the Realm API then I’m not sure what else is left in your app that necessitates a separate data store and ORM.