The tail scale recommendation is a good one and you can get around the three user problem very easily by simply using same user account for every device. You could have for free up to 100 connections with the same account ID.
If you’re trusting the person to access a server inside your house then you can trust them with your user ID and password to tail scale.
If you would prefer total separation of user ID and password the nordvpn free meshnet is another good option that I have deployed for friends and family.
Adding to what @Wank said, an additional option instead of adding users to your Tailnet is to individually share devices which don’t count against the 3 user limit on the free personal plan.
Each of your friends would install the Tailscale client; register their device(s) as prompted; then accept your invite to share a device. In many ways, the process is similar to Syncthing’s.
Bonus benefit is that you won’t be opening up your entire home network by tunneling everything from your friends’ home networks.