My wife's iPhone rings when I get a call on mi iPhone... How do I stop this?

The RIGHT way to do it is to get separate Apple IDs for you and your wife, and then connect them with Family Sharing. The next best way is what Chris has suggested.

Sounds as if you are both logged in with the same iCloud ID. If that is the case, on both devices, go to Settings>Phone>Calls on other devices and turn that off.