my family which compose of 3 adult and 3 children, will travelling Hong Kong by November this year.

According to the weather records, it is cool and cloudy at that time, the average temp is about 71 Fahrenheit degree. You should wear long-sleeved shirts, thin coat and pants.

Yes, the octopus card can be used both on bus and MTR. And surely you should buy the card, for it is very convenient and you can get a discount by using it.