You can use different accounts for different Tv boxes or else you can even use the same account for all Tv boxes.
When you connect two different TV boxes with the same account, you can purchase a vudu.com/start movie from one Tv box and watch it on a different TV Box in your home.
Your VUDU login will not be synchronized automatically along with all tv boxes, you have to log in separately on each TV box.
If you purchased a vudu.com start code movie by mistake, no refunds will be provided by Google Fiber. You can contact VUDU for all the purchasing issues if any.