We (5persons) will visit HK for 1 week, and use Express Tr. Which is best card to use for each?

According to your situation, you are advised to purchase the Standard Octopus Card. Each card can only be used by one person. For adult, the deposit is 50 HKD and initial stored value is 100 HKD. You can enjoy some discount when taking public transportation.
In addition, in order to save money, you also need to buy the Group Tickets of Airport Express. The tickets of 'Group of 3 + Group of 2' would be great.
Hope helpful!

Thank you very much. This means that we will buy 2 types of cards .first type is standard one( 5cards) and second type is airport express group (2 cards different group )
Right?

Yes, you are totally right. :)