Homeschool World Forum

If your children are self motivated to study things like physics, Mozart, meerkats and DNA on their own in depth, I'd say you have done your job well!
Do you know about unit studies? Your kids may love them. In fact, it sounds like your older ones may be desiging their own already.
I think keeping the math, writing and language requirements is wise, especially if they are college bound. It sounds like they will probably cover the rest on their own given the opportunity. You can begin to work all this independent study into a standard transcript format (for your high school age kids), and have them fill in any "gaps" they see for minimum college admissions requirements if that's their goal.
Congratulations on a job well done!

Can they pursue dual enrollment at a local community college? If they have already learned much of their high school material, many students do this. They will learn college level material will still getting their official "high school credits" They may be able to do this online. Also, many colleges have free classes online; you can listen to the lectures and such for no charge. Look for online learning on a google search.