Access to lounges are based on the class they are flying in. It doesn't matter if they've been booked by award points. They will have access to any of CX's lounges in HK and SFO. But best if they stick to the ones closer to their respective gates they are flying from. The CX agents in HK will tell them where to go.

Yes First class is the ultimate way to travel, in the lounges and in the air. Perhaps you can do one way in business and one way in first for your folks. Otherwise you may just save it till the next trip. You would't want to spoil them so much that they'd never want to fly in coach ever again, eh?