UEFN disable building half works. Still get ghosted structure pressing Q.

That is disappointing, the settings should work, you should submit a bug report, go via the Help menu - Report Issue in the editor it’ll give a code and take you to the report page. Hopefully this will get fixed soon.

As for the player spawning in the wrong place, do you have a spawn point per player, sharing them may cause issues.
There are island settings for

Not sure about disabling Q, Verse may be able to but I don’t know.

This thread discusses it, I added a vote there