We arrive in Hong Kong on Sunday morning and leave early Tuesday morning.

Well, according to your situation, you are advised to purchase the Round-Trip Airport Express Travel Pass. This card contains two Airport Express single journey(s) plus 3 consecutive days of unlimited travel on MTR (except East Rail Line First Class, Lo Wu and Lok Ma Chau stations), Light Rail and MTR Bus (Northwest New Territories). After purchasing it, you can rechrge some money on the card. Then it can be used as the Standard Octopus Card. The fare is HK$350 respectively (with HK$50 refundable deposit). Notably, one pass can only be used by one person.