Nine-character group scene in living room background

Please stitch the file I just attached into a 3×3 grid to make a horizontally long file. After merging, resize it so that the long side is long_side_px_en pixels while keeping the aspect ratio. Set the quality to 100% (maximum quality) and output as a JPG. Using the background from the first attached image (background_en), place the nine characters from the second attached image (the character sheet) so they are spending time peacefully in the living room, for example sitting on the sofa, looking at the photos on the wall, picking up books, sitting on the floor and chatting, and so on.