Where are you using the devices? And not all devices are easily interchangeable between countries so that could be an issue. Have you tried recalibrating the location in maps? Honestly, though, everything goes through the Nest/assistant app, and the weather format is set in the Assistant and it's not possible to have two options set in assistant for the temperature unit. If one is set correctly the others should be set the same.
Have your tried factory resetting the devices that seem to be set for the U.S? Something isn't quite right somewhere in the setup or on those devices. The phone determines location and that's sent to the cloud account and fed back to the system, especially since they are all presumably on the same home WiFi network and user account.
