In Hong Kong for 4 days from this Sunday morning and there will be 5 of us staying in traders hotel.

According to your situation, you are suggested to buy ordinary Octopus Card.
From the airport to the hotel, you can take bus no.A 12 at Airport (Ground Transportation Centre), get off at Ka On Street, Des Voeux Road West. Then walk west around 300 yards to get to the destination. It costs 45 HKD per person.

If your child is under 3 years, he or she can enjoy the free ticket.
If your child is between 3 to 11 years, he or she can enjoy the half price ticket.

In addition, for adult, the deposit is 50 HKD and the initial stored value is 100 HKD.
For Child, the deposit is 50 HKD and the initial stored value is 20 HKD.

As for four days sightseeing, you can recharge 100 to 200 HKD for per Octopus Card in general.