can i setup my apple watch cellular with my wife's phone?

To clarify, yes, you can but the results will not be good. As Chris noted, you will get her calls, her messages and you would only be able to manage the watch from her phone.

I'd suggest that you cancel the cellular service on the watch and and use it with your phone with BT/WiFi.

That isn't possible. Since your Apple Watch is connected to your account and your phone it would have to be on a plan that is already connected to your phone.

If you did, it would have your wife's phone number, you would receive all of her calls, texts, etc.