Whether or not the fat family will be required to ultimately pay for the second seat is to be determined, but I'm guessing Southwest will not ask for payment due to the publicity of the case. The skinny woman will be offered a $300 voucher, probably put up more of a stink, and end up getting a couple of free trips out of it. The blame for ALL OF THIS lies with the fat kid's parents...assuming this kid is not sick in any way, other than having an addiction to Doritos.
‘Clearly the obese kid did not pay for 2 tickets, otherwise there would not be a seat to release to the standby skinny lady’
That’s all that needs to be said. If you can’t fit in one seat, buy two. I think airlines should have weighscales too, if you are over x pounds you pay extra.