The security line is usually not very crowded at that time of the evening. There are usually two (sometimes three) flights leaving from G concourse in late evening: BR to TPE, UA to SYD, and SQ to HKG.

Unless the connection is very tight, they should not have a problem.

NB: America West arrives on the other side of the airport from Intl G. They should go into the Intl terminal via the A side connection to Terminal 1 and cut through behind the check-in counters to get to G concourse check-in. Going outside and using the Aerotrain will probably end up taking more time.

It's up to them whether they would rather walk or ride.