First, congratulations.

I did this trip 6 years ago with my sister to get my niece. We were very lucky and the air tickets were given to us, along with upgrades from friends (all on UA).

I know that NWA used to offer special adoption fares, check with them.

If all of your friends have miles on the same airline, then I would call the airline and see if maybe they will waive the fees and arrange to transfer the miles into 1 account so you could at least get 1 ticket free.

You said you needed 3 tickets, so I am not sure if 3 of you are going to China, but the baby can come back as a "lap child" as long as she is under 2.

Good luck!