In the Titanic book on page 22 the text states that he didn’t fully seal the top of the watertight compartments. Now that's one of the first things that I would check. Also on page 22 He made it so that water could fill the first four watertight compartments. But as I talked about in the sentences before he didn’t seal the tops so water flowed right in every compartment.
I also believe that it was the captain and the crew members.It says on page 19 that they radio operators were supposed to keep the radios going twenty-four