Its a lot simpler then that. Dont add them to your tailscale account. Each user should have there own tailscale account. Then you just send them a link to share your machine (your server) with their tailnet. Then all of there devices they have added on their account can access your server.

Bonus: send them referrals and you get your device limit increased when they make a account. Which all the have to do is sign in with google or apple.