Is your UO flight booked under the CX code? If you are not sure, are you connecting from a CX prime flight (CX-coded, CX-operated flight) on the same ticket? If you did not buy the CX code-share, you do not have CX lounge access yourself at HKG. If you did buy the CX codeshare, although the rule did not go as specific, I believe you have no problem guesting 2 people on any CX flight.