Can I see which families have not booked yet?

Not as a list. SchoolConferenceGo does not compare bookings against a student roster.

What you can do: click Invite families on a night that is open for booking. It counts the parents in People who have not booked this night and lets you email them the booking link in one click. Families already booked are left out automatically, so you can send it again later as a nudge.

To see who has booked, use the Bookings list on the night page or Download roster (CSV) on Reports.