By placing all your RokuTV's on the same account, you have "linked" them to one account. If you add or remove a channel from one device, it will add or remove from all devices. If you purchase a subscription directly from Roku, it will be made available to all your Roku TVs. Parental control and PIN numbers will also be synced.
The channels and Roku subscriptions are linked to the account. The individual settings are specific to the Roku device though. You will have to configure each Roku device regarding menu layout, backgrounds, channel/app layout, and sign-in/authenticate to all non-Roku subscriptions on each device initially. If you move a channel to a different location on one device, it does not follow or affect your other devices.
There currently is no way to automatically mirror and sync non-account actions between devices. The only thing that will be account wide is access to subscriptions, channel adding and removal, and any preferences you set up in your online dashboard like parental control and PIN numbers. (https://my.roku.com/account)
Essentially, the Roku devices do not interact with each other. Only changes made within the actions linked to the account will have an affect on the other linked devices.