This happened to us on the Safari too. We were a party of 6 (4 adults & 2 children) so the CM split us into 2 rows. Me, my mom, & DD6 were in one row and DW, her mom, & DD2 were in the row in front of us. After we boarded, the 2 adults in line behind my MIL came up and squeezed into the row with them. I don't know if they just didn't see DD2 in between DW & MIL, but they asked my MIL if she could move over a bit. She politely said no & pointed out DD2 sitting next to her. At that point I thought the couple might realize their mistake and get off, but they didn't. It can't have been a very comfortable ride for them but its their fault for squeezing in when it wasn't their turn!