Can Apple Watch and iPhone work on different esims

The Cellular + GPS Apple Watch has an eSIM and shares the iPhone's phone number, and the carriers that support the Apple Watch charge a monthly fee. In the U.S. the fee is $10 per month. Here is a list of carriers that support the Apple Watch:

https://www.apple.com/watch/cellular

While not as useful, there is Apple Watch Family Sharing, which is intended for a dependent child, where the Apple Watch gets its own phone number, and the Apple Watch is managed by the parent's iPhone. In this mode the Apple Watch has less features, as anything that would depend on information from the iPhone is not available to the dependent child.

https://support.apple.com/guide/watch/set-up-a-family-members-apple-watch-apd54d0a51fb/watchos

https://www.apple.com/newsroom/2020/09/apple-extends-the-apple-watch-experience-to-the-entire-family/

Also Family Sharing cellular plans are more expensive than pairing your Apple Watch directly to your iPhone.