There are two ways to share an add-in. The first is what @kandennti suggested you use a file service or a network drive, and everyone references the add-in folder from there. The second is that you provide the add-in files to the others, and they install them on their machine.
The advantage of the first method is that everyone is using the one-and-only set of files, so when you make any changes, everyone automatically picks them up immediately. The negative is that you need to be connected in some way.
The advantage of the second method is that you can share the add-in with anyone by emailing it or providing them a way to download it. You can also package your add-in into an installer to make it easy for them to copy onto their machine. I highly recommend Inno Setup. It's free and is very powerful.
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Brian EkinsInventor and Fusion 360 API Expert
Website/Blog:
https://EkinsSolutions.com