Wow . . . a lot of emotional decisions to make, on which I am no expert.
On the business side though, my suggestion is to run the existing company, turn it into something great and then sell it and fund your new idea. Remember: The biggest challenge with running a family business is the question of whether senior family members let you run it as your own.
If not, then go do your own thing.
From a pure financial viewpoint, you will generally make a lot more money a lot faster over-hauling an existing average business than you will starting something from scratch.
All the Best
Tim Berry is the chairman of Eugene, Ore.-Palo Alto Software, which produces business-planning software. He founded Bplans.com and wrote The Plan-As-You-Go Business Plan, published by Entrepreneur Press. Berry is also a co-founder of HavePresence.com, a leader in a local angel-investment group and a judge of international business-plan competitions.