Complex sentence: When the boy rings the bell, both he and Sarah marvel at its beautiful sound; but because their parents neither believe in Santa Claus nor the spirit of Christmas, they do not hear it and remark it to be broken.
Split into simpler sentences: When the boy rings the bell, both he and Sarah marvel at its beautiful sound. However, their parents neither believe in Santa Claus nor the spirit of Christmas and do not hear it and remark it to be broken.