what is the best mode of transport from Shenzhen Airport to Metropark Hotel, Shenzhen, 4 adults?

From Shenzhen airport, you can take subway Luobao Line to Laojie and transfer to Longgang Line. Get off at Shaibu station and then walk to the hotel.
From the hotel to Hong Kong, you can walk to Shaibu to take subway to Laojie and then take Luo Bao Line to Luohu station. Then walk to pass through Luohu Border, you will get into Hong Kong.
The average hours required to cover those places is about 2-3 hours in my opinion.