Yes, you can join friends within X-plane 11
Google, "Whats my ip address" note it, get your friends to do the same, share. On the Settings/Network Tab, upper right, input your friends ip addresses adding a line each. Get them to do the same.
You may all need to open UDP port forwarding on each router/firewall (49000-49010) - check youtube for your models, if you dont know how. Allow Xplane11 through your firewalls.
Ensure you all disconnect xSquawkbox and iVap using PluginAdmin (Upper Left Dropdown Menu) simply untick.
LR need to invest a little work as currently multiplayer doesnt send livery data.
Hope this helps