We stayed in the LM rooms last November with 3 boys. I didn't find them girly at all. My boys didn't complain. Show them some pics of the inside of the rooms and see if they like it.
My 11 year old boy was not bothered by the theme. If your grandsons want the pool I would say stay there. It is by far the nicest pool on value property. The pools are fenced off as well.