Stop text messages on multiple devices.

Madman69 wrote:

My text messages appear on multiple devices. They show up on my wife's and son's phone. How do I stop this?

This happens because you are using the same Apple id for imessage. On their device go to settings - message - send & receive - remove or uncheck the Apple id.

They should have their own Apple id to use for imessage and facetime.

Stop sharing Apple IDs on all devices.

Setup and use Family Sharing instead.