Hi @ruhbehka. Great question.
OK, so option 1 is the best from a technology standpoint. Your guests go on your real wifi and Koala is not involved. If you can solve the earshot issue, that's the way to go.
The second option of having the "Everyone Else" profile in parent mode also (sort of) works. When KoalaSafe is in parent mode, it doesn't log anything. As you rightly pointed out though, if your child's friends join, they would automatically go into Parent Mode, so no, that's not a great option.
In answer to your question about your kids devices being forgotten... no, it doesn't work like that. If you've put them in a profile, they'll stay there.
So, I think you have two real options for your guests:
1) Your main network (with whispering!)
2) A "Adult Guest" profile in KoalaSafe in Parent Mode.
When a guest arrives, they join KoalaSafe and you move their device to that profile. Because it's in Parent Mode, you see no monitoring.