Do we need Transit visa for Hong Kong

Hi Team,
My parents are travelling to Nepal from Sydney on 28 Nov 2018 on a Nepalese passport. They are travelling via Qantas to Hong Kong and from Hong Kong to Kathmandu from Kathy Dragon. They have transit at Hong Kong airport for 3.5 hrs.

Please kindly advise if they do need transit visa and how can they apply and how soon the entry permit can be issued?

Appreciate your prompt assistance and thank you very much in advanced.

Regards,
Sailesh Wagle