The better way to mange 2 production CMs?
This becomes case of Global or regional bom, More centralized for managing CMs. not distributed at site specific. For Managing centralized configurations, Ensure
1) Parameters associated with Manufacturing, Sourcing, Quality and Design are having common stake holders to arrive at Review and Release of ECN. This make sure ECO is effectively implemented and concurrent reviews are done collaboratively.
2) Alternavtive, Make one CM as partner to other CM and drive the change through one CM.
I think your implementation is based on the relationships you have with your CM. One aspect my start with access to Agile and then Security access to View Objects. Who can view what and, should they View each other?
At a simple level you may choose to have a common BOM with ECO used to manage the content. If an assembly or part needs a revision it needs a revision everywhere. Then, use MCO to address manufacturing issues – either at all locations, or with an individual CM.