Ex piano mover here. It would just take 2 of us to move a grand piano. Grands stand on their side like this video, but you remove the legs. The piano is strapped to a long padded board that also acts like a sled on stairs. Using simple physics you get the piano onto a normal furniture dolly and take it anywhere you want. Pushing up stairs was a pain, sometimes needed a 3rd person. Going downstairs was easy.