Some of the google devices show "Offline" although are controllable through the google home app. Restarting, powering off, etc. procedures do not have any effect. The most interesting part is that those devices show "Offline" in the owners google home app but show "Online" in all the family members and guest google home accounts.
Super weird, no?! What's up with that Google?
That certainly hasn't been easy for ya'll ― let's check it out. A few questions: is the owner the one who added all the others as home members using the Google Home app on his phone? Is the voice command working? What are the Nest speakers affected by the offline status? Are all the devices on the same Wi-FI network? It would help a lot if you could do a sequential reboot first. Unplug the power cord of your router followed by your Nest speakers. Plug them back in after 3 minutes tops. Restarting your phone might also help.
Also, could you double-check the account on his Google Home app if it's the correct one? Try reinstalling the Google Home app and tell us how it goes.