Flyimg Katmandu to Kunming China to Shanghai to Los Angeles

Flyimg Katmandu to Kunming China (11hr layover) to Shanghai (2 hr layover) to Los Angeles
Time in China less than 24 hrs
Ticket folks say I need a transit G because I'm making two stops.
No transit one for Kunming airport.
They suggest alternate flight with less attractive flight times, with only one stop.
Can I just stay in Kunming airport and avoid need for transit G?
Do I really need a transit G if I do not leave airport?
We are USA citizens