Activating Apple watch on stand alone line

I had a question concerning setting up an Apple watch on a stand alone line. I purchased the Apple Watch from T-mobile and was required to add a new line. I did and the watch was mailed to me and can see an additional number in my T-mobile account. However, the watch is not functioning as it is supposed to so I am assuming that we do not have everything set up correctly.

My wife has paired the watch with her phone. But when I call her cell number the watch doesn’t ring or anything. When I call the number that was added to my account, the call goes right to voicemail. But the funny thing is my wife can make calls from the Apple watch and the caller id shows her cell number number but again she can't receive calls on the watch.

Is there something we are missing with the activation process of this Apple Watch and new stand alone line?