Advice on technique for manipulating picture

I’m new to Blender and drawing programs. I’d like to remove the chairs and the little Einsteins from the picture and make the panel etc. complete.
First off, is the picture 2D or 3D? How would you go about what I want to do and with which program?

I don’t fully follow you- all pictures are 2D by definition. Are you asking if the image was originally created in 2D or 3D software? 2D for sure, my guess would be ToonBoom. The backgrounds were done by Veronica Jones, who is a 2D artist with experience in traditional and digital background painting

Oh, my bad. The series is a blend between 2D and 3D, got confused by this.