From the moment they entered the throne room Magneto had an electromagnetic shield up that he extended to include his ally as well. Common courtesy. He felt through the room for metal, finding it in the Doom Bots littered among the bodies of the guards. In a pinch he could deconstruct the robots and use their metallic parts as weapons.
There was someone in the laboratory but 'alive' was a relative term as the men soon learned as they paused In the doorway. There was a single Doom Bot cowering in a corner of the room muttering something to itself over and over.