I'd base your invitations and attendance layout on Meetings with a portal to MeetingParticipants that includes at least a name field or two from Participants.
Invited and Attended can be number fields formatted as check box groups with a single value check box that enters a 1 when the box is checked. you can resize the field so that the 1 is not visible, just the check box.
Your post suggests that you want a quick way to mark groups of records as "invited" or "attended", but I can't quite picture how you want the user to identify such a block in the interface so that a block of meetingParticipents records are so marked.
A "Mark all" script could be written that either loops through these records or that uses Replace Field Contents to mark them.
It might be possible to set up the check box field's as a button that checks to see if a modifier key such as the Shift key is down when the field was clicked. If it's not, the script can modify just the current record's attended or invited field. If it is, it might log the current portal row in a portal. when a second click with shift key down is pressed, the script can loop through the rows and mark all the records from the first row shift clicked to the second portal row so shift clicked and this could work in either direction in your portal.