Group Airport Express or Express Travel Pass in Hong Kong

Hi - We're a family of 5 travelling from the airport to Harbour Plaza North Point (Quarry Bay). We'll be in HK for 3 days and have one child under 11. Are we better to get a group of 4 ticket and a child ticket to get to our hotel or buy 5 x Airport Express as we'll use the MTR during our stay? Also can we get a shuttle bus from HK station to our hotel on a Sunday evening? Thanks