Apple series 4 watch

The Apple Watch shares the iPhone's phone number.

If you have a Dual SIM iPhone, then you can arrange to associate the Apple Watch with one of the alternate phone numbers, but you will only have 1 active on the Apple Watch at a time, and you will be paying the carrier for the Apple Watch support on each line you want to have available on the Apple Watch, even if at the moment you are not using the other line.

https://support.apple.com/en-us/HT209043

No, you have to sync one number to the watch from your carrier. Your watch has a number too technically but it really is just there for billing purposes. You can sync two watches to one number, at least on ATT but not two numbers from two different carriers on a single watch. That is not how the sync works...the iPhone is needed for that purpose.