Hi! Fastest way is to go by taxi especially since you're arriving late at night. It will probably cost you HKD120-150. There's always a taxi available. It will also save you from transferring from one train line to the other since taxis drop you off right at the lobby. Just make sure to tell your driver which hotel you'll be staying (disney hollywood or disneyland hotel).
Checking in would also be a breeze since there's less people at the lobby :-) Try to also ask the front desk for the express pass in disney since you're booked at the hotel. It will save you lots of time in the rides' queue at the park. Enjoy your stay!
The standard rooms are normally 2 x Queen beds and it would be a squeeze however best to contact them directly giving numbers,ages etc as from their many room options they will certainly help with the best and most cost effective solution and if they did have rooms containing 2 X King beds this would likely work for you.
There is a storage room just outside the lobby. Cast members are happy to assist. As most check ins are at 2pm and people arrive early to go to the Park, the storage area is quite large and most store luggage and collect after their day at Disney!