No your entire party doesn't have to be there. The hostess just confirmed ages at check in, 2 adults, 2 kids. We had breakfast at Ohana at our last trip, we checked in at 9am for a 9:05am res. We didn't sit until 9:40am. If you do the breakfast and kids want to see Stitch, the way it worked was we checked in, got a buzzer and stood in line to meet stitch. This day, Aug 15 this year, Stitch didn't come into the restaurant, he was posted out front. After we met him (it took us 10 min to get through the line) we walked around the lobby at the Poly a bit. Sometimes I think stitch comes inside the restaurant. I will say walking around the lobby or just outside is your best bet. If they are back at the room, that could be a haul.