I'm with the "go for it" group, which seems to be everybody but your brother. Not having any experience, except for a few overnight rides as a teenager, I can't offer much advice. Some sort of conditioning schedule would be advised, as well as trying out anything new -panniers, rain gear, bike shorts, whatever, before you go. Don't forget detailed maps, and maybe get any LBS numbers along the route, in case you have more than just a flat.
Too bad she wasn't moving to NJ, I'd love to ride part of the way with you!