I think that talking about height is really funny, but I wanted to clear things up. The girls from last year's tour were really stair steps with Grace & Amanda almost exactly the same height. The Molly was definitely the smallest. I don't think it matters, but it did look great on stage.
They were in order tallest to shortest
Maddie - tallest
Abby - was just slightly taller than Grace
Amanda was slightly shorter than Grace.
See this picture on the top. They all grew a couple of inches by the end of tour, but all about the same so they always were consistent on stage.