I would prioritize your 401(k) over the 529s. That's a lot of tax money you're voluntarily paying by leaving that space unfunded in your 401(k). If you wanted, you could use the tax savings from the 401(k) and contribute that to your college savings plans. Given your plan to be earning extra income when they're in college, the EFC contributions from the 529s are probably somewhat immaterial compared to other considerations. The tax benefits of 529 plans are most significant with contributions made far before college; contributions made only a few years before withdrawal won't give you a whole lot of tax savings anyway.
Simple example - $10k grows to $15k over 6 years at 7%; Tax savings would be approximately 0.15 (capital gains) * $5k = $750 in 6 years.
Tax savings on $10k contributions = $2200 immediately, or the equivalent of $3300 in 6 years.
Yes, there were a lot of assumptions in that simple example (tax rates, ignoring state taxes, dividends, etc.), but hopefully you get the point.
If your state gives you some benefits for contributing to 529 plans, that is worth considering as well.