As suspected by all, FIL stuffed up! The fares he was quoted were per person.

Consequently I now have them on a DCIRC26 SYD-LAX-ORD-CLE-LGA-SFO-HKG-SYD for AU$8,269 +US$75 for an additional US stopover + taxes. They are also going to take a NYC-BOS-Canada-NYC 10 day coach trip

FIL thinks I am a genius and even the MIL is smiling!

Thanks for all the comments and assistance. Feels somewhat bizzare that the first major trip I have planned with help from FT isnt even for myself!