a minor travelling to hong kong with a 21 year old for the first time

Would just want to ask for the requirements for a 17-year old minor to be allowed to travel with his 21-year old cousin for a 2-day vacation to Hong Kong this December. This would be the first International travel for both parties. I am Ms. Darica Joyce Beltran, the Brother of the said 21-year old and I am supposed to pick them up at the HKIA when they arrive.