Currently if you have Norton Security Premium, a seat is taken up if you install the Norton Family Android app and set it to parent mode. Given that one is not getting any protection from the app in parent mode (as its simply a portal into the website), there should be no seat taken. If it was in Child mode then sure, take a seat, as you are getting some protection from it.
Feels a little like false advertising to say that you can have protection on up to 3 devices when actually its only 2 if you install the parent app on your phone (but no other Norton app).
Richard.