Hong Kong Transportation Matter

We are a family of 6 (3 adults, 1 elder (age:77), 2 children (age: 2 and 4)). We are taking airport transfer (to and fro) from HK MTR Station. We will be staying for 6 days and will be visiting Disneyland, Tai-O Village and various shopping areas near Tsim Sha Tsui.

The only exception place to visit is Sai Kung Seafood area. As such, should I be getting the Octopus Card or the tourist day pass? If the recommendation is the Octopus Card, how do I purchase the limited edition type? is it sold at the Airport Express Counter and all MTR Stations?