Please advise -
what would you do in this situation?

I'd start making phone calls (or sending emails). It's not at all rude for you
to follow up, particularly if you can pull off a pretense that you're afraid
something has gone wrong with the mail and the invitee must not have received
the invitation, about which, of course, you are so sorry.

It's much more likely, of course, that the invitees have simply blown off
responding; it's sadly a common phenomenon. No less annoying for being so
common, but there you go. You don't have any way to predict how many of the
non-responders will show unless you've got some past history with these
particular guests to go on, so call.

Holly
Mom to Camden, 2.5 yrs