The problem with having multiple devices ring when you get a phone call is an easy fix and not related to digital touch.
Try this: Settings > Face Time > iPhone Cellular calls to Off on their phones.
Now, my wife and I have shared an AppleID forever and we both now have apple watches. And, yes, the DT does the same thing for us, whereas we can iMessage each other just fine without issue. DT needs to be tied to the same email we are using with iMessage and this won't be a problem. Until that happens, we just have to get used to the fact that DT will send to both the sender and the receiver if they are sharing the same AppleID.