To get the feather on top of the fireplace, you must do a parkour. This parkour starts in the corner of the room, over 3 floating books. Then, you must use Leviomora (a spell in your wand) to lift the blocks with wings on the ground, and then jump on them! Once you've lifted 2 leviomora blocks, there's 3 more floating books to jump on, which will lead you straight to the feather on the fireplace.
Hopefully this helps, and reply here if you have any more questions