As with any location, I believe there is a certain risk. Let me put a disclaimer that I am not promoting trespassing of private property and by doing so you will be responsible for any consequences. The Istana Woodneuk is pretty much isolated but there is a steep hill to climb with thick vegetation so getting there is difficult. Once there, I believe no one will come to disturb you. However take note that there is a guard house with a security person about 500metres away from the Woodneuk itself. I'm not sure whether there is a guard stationed there all the time.
The Brunei Hostel is in a residential neighbourhood and it is surrounded by houses. Bringing heavy video equipment is likely to attract the attention of the residents in the area. I quietly went in with just my camera and one of my friends so nothing happened.