If you book less than 12 people on a lane, and do not book a private lane, you may be placed with other people NOT in your group.
The only way to ensure that your group is alone on a lane is to click the “Private Event” option. To book a private event, when you click the “private event” box, you must pay full price for 6 people, even if you have less than 6. Any players from 7-12 are full price at $30pp.