I'm just about to send out my own graduation announcements, and I agree--they are very confusing! I even thought at first that they were invites. My family did point out--the four tickets we received are for reserved seating. There is general seating, which is good because both of my brothers, who graduated from my old high school, had my grandparents and a couple aunts and uncles (in addition to the four tickets) at their graduation ceremony.

And I think even if you would have actually invited them, they probably wouldn't go. Nothing against you lol but like you said, most people don't want to sit through a graduation ceremony. People just like to be thought of and included. At least, that's my take on it.

Congrats, and GO SEN10RS!!!!!!!!!