After you've created a meeting (click this link if you want to learn how) you are able to see who's accepted and declined your meeting.
Simply go to the event in question, click it, and you'll see either a question mark, a red X, or a green check mark.
A question mark means they have not accepted or declined. They've probably not checked their message yet.
A green check means they accepted your meeting and it's been added to their calendar.
A red X means they have explicitly declined your event.
You will see Samantha, David, and John have all not see (or ignored) my meeting invite.