at last i got it sorted out.
we can open a private game and invite friends directly.
i created a password too. but it showed that invited friends need no password for joining.
invited friends will get invitation notifications and can join without being asked for a password.
and no unknown players can join.
it's even flexible because a mix of invited players and other players (with pw) is possible.
so we have comfort and protection. great!
dummy me just needed some time to check it
@JaneHatke and @Mirefox, did you get invitations to Great Mosque SP?
(if not you can join by using pw: oncemore)
zen4one and zebracadabra have already joined the game.
so Great Mosque SP is the official 5-player tourney game now.
what to do with running 4-player game "Great Mosque"?
shall we go on as friendly exercise game?
guess we can never play too many games of Istanbul, right?