please give us your suggestion if we all are 16 people want to holiday inn hotel causewaybaym Hk

For your hotel, you cannot use the free shuttle bus from HK Station to your hotel.
If you want to take the airport express, you can take it to reach HK Station and then you can walk to Central Station where you can find the Island Line to Causeway Bay Station. You can get out of the station from Exit A and then walk to your hotel.