I have a Verizon MiFi we have to turn off daily that sends the signal to a main router, and then theirs a second router that's hard wired to the main router; which the nas server is connected to. My question is can I set the server to be accessible with out Internet on all of my computers?
I apologize for not answering your question properly. The answer is Yes. Internet connectivity has nothing to do with FreeNas functioning properly. In your case though since you have multiple routers on the network, only the computers connected to the 2nd router (the one that FreeNas is connected to), will be able to see the FreeNas. At least until you either flatten your network (change router #2 to a bridge), or port forward (or static route) through router #2.
Your post #1 and post #19 appear to be conflicting. One says wired, the other says wireless.
So to ask you a question. Can you please provide a network diagram, including physical connectivity, IP addressing (including IP space and subnet masks, as well as DHCP servers), and where the client devices are located? You can just draw it on a piece of paper and post a picture or use something like Visio.
Thank you.