How do you pass those square things with the ice bridges in the chamber..

First use Ron's deluminator on the lamp nearest the entrance. Then control Hermione - walk straight using the pressure pads, when you get to the second or third platform the bridges should lead you right, go up the right hand side being careful not to get killed by the blue darts the snake heads spit. Hit the pad next to the snake head on the right, move Hermione out the line of fire and then switch to controlling Ron. Follow the path you made with Hermione (don't step on the pads again as the bridges will change) HOWEVER when Hermione went right, use the pads to go left. There is another snake head in the top left hand corner which you need to stand on to make the bridge appear for the final platform. Ron can illuminate the lamp from here too which will open the gate. Carefully retrace your steps without standing on any pads and walk over the final bridge to the gate. It's easier if you use the map in the top DS screen.
Hope this helps.

I can't get it I get hermine where she's need and ron where he's needed I step on the pad then out of the way so I don't get killed but when I retrace my steps the bridge is not there HELP PLZ