How to define the order of reducers execution in Redux?

Is it possible that component C were rerendered when R1 is executed but before R2 is executed?

No, it is not possible if you use a single store like Redux docs suggest.

In Redux, you combine reducers with combineReducers(). This means that from Redux’s point of view, there is only a single reducer, and it is synchronous. Sure, it calls your two reducers, but the Redux store only begins notifying subscribers after it gets the new state value from its root reducer, so it is guaranteed that all your reducers have already been executed by the time the views are notified.