Ones I have a paid an app membership can I access it on multiple TVs at the same time in the same network
It depends on the provider. Some providers, like Netflix, limit the number of simultaneous users.
I need an answer to this question also but I can’t find it on this platform. How can I talk to a live person from Roku to get an answer?
As mentioned above, it depends on each content provider. You'd need to check the policies of whatever providers are you are using.