There once was once something called an "Infinite USB Memory Drive" that acted as a thumb drive that read and wrote data to a networked share over wifi.

They aren't selling those anymore, but their approach might be what you need - network share to handle the multi- device connected to same drive issue.

In your shoes, I'd be looking at a Raspberry Pi Zero W (the one with wireless) instead of an arduino. More computing options means more ways to solve your problems with the same hardware.

There once was once something called an "Infinite USB Memory Drive" that acted as a thumb drive that read and wrote data to a networked share over wifi.

They aren't selling those anymore, but their approach might be what you need - network share to resolve the issue of multi- device connected to same drive.

In your shoes, I'd be looking at a Raspberry Pi Zero W (the one with wireless) instead of an arduino. More computing options means more ways to solve your problems with the same hardware.