I agree with those who say to definitely keep it obvious that it is about a bike ride and the route. No offense, but I wouldn't really pick up a book to learn about a mother's fears of doing the trip. Yeah, I'm a guy, but I'm a dad, too. I wouldn't be drawn to a book about a dad's fears, either. If the book is well written and the inside story theme is how you, as a mom, saw the ride, then that's all good and would keep me reading. But putting that in your subhead seems to be limiting your audience on what is already a book with a somewhat limited audience.

Title ideas:
1. The Very Long Road
2. We did it!
3. Pursuing the Impossible

Sub ideas:
1. Inside a family's dream to bicycle from Alaska to Argentina
2. Two kids, two parents, and 17,000 miles by bicycle from Alaska to Argentina