The simplest would be the Herk7769 route. It allows you to work with or without the internet. You will need to download and store the videos, and streaming files to your network storage.
Everyone will have access to it and the network will adjust as you are within range of an internet connection or not.
If you want all the bells and whistles and aren't very tech savvy, try this site:
How to Set Up a Home Media Center & Network - TV & Movies on Demand
it does a pretty good job of telling you what you need and how to do it. It walks you through setting up a whole home media network (it ain't cheap). You can look around for other products (hopefully less costly), once you see how they all connect and what they do. Not endorsing any of the products, just giving you the information.
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Ben and Doreen
Home Away From Home - 2017 PT Crusader 315RST
TV - 2016 Ram 3500 Laramie 4X4 6.7 Cummins Diesel
Never Enough Time Camping!!