I like the cover a lot. It shows very concisely where you went and how you did it. The title seemed overly long at first, but it's growing on me more and more. I think you don't need the re-mention of family in the subtitle- you already know it's one family from the title. BUT you won't know the locations or method of travel from just a library search, so that seems important in the subtitle to me.
Maybe something like
One Family, One Dream, One Very Long Road
A trip of Discovery from Alaska to Argentina by Bicycle
I really liked the "A tale of bicycling and discovering" suggestion.