My family is returning home tomorrow on AAEagle. We're 5 people on 1 PNR. My 15 y.o. son got a last-minute offer to stay with family for the week, and then he's flying home on Southwest (due to 2 airport changes needed to make it work). Will we have any issue only checking in 4 people online, or showing up tomorrow without him? I've never thrown away a return ticket and don't want any unexpected problems/charges? Thanks!