I agree with foobar and fixer on their points. On fixer's, you are better off even if you pay the same rate, but hopefully you won't have to, see below. On foobar's, if you can live on less, you can stop working sooner which will give you more time to convert, and it will give you more exemptions/credits (Kids) to do it with.
If you can convert while you still have 2 dependents, particularly with child tax credits, education credits, and anything else you can find, this will accelerate the amount you can convert.
You can do about $10K/year tax free as a single person. Married filing joint goes up to about $20K. Having 2 kids adds another maybe $5K/kid, but it could be more if you're paying for college. Having other big deductions like mortgage interest and charity can help as well, but that's tough to do while living on less income.
A few other tips:
1) Stay within the 15% bracket. This has many advantages, but at the very least you're saving a net 10% on all this income due to the reduced rate. With a married couple, you could convert around $94K/year, take the standard deduction + exemptions, and you'd be just inside the 15% bracket. Combine this with using the funds you've already saved in Roth and you should have plenty of money to live on.
2) Convert depreciated assets - market timing essentially. Pay close attention to trends, and try to convert when your assets have lost value. You pay the tax based on the value of the holdings on the date you convert them.
3) Capital losses - I didn't see you mention anything held in after tax brokerage accounts. If you don't have anything there, get some funds invested there to use for this strategy. You can harvest capital losses and use up to $3K/year to offset TIRA to Roth conversions.
4) Take advantage of any disasters - I had a client who lost a ton in a real estate deal. He ended up with a $500K loss on his 1040, which carries over to the next year. We used that, and a huge dip in the market back in 2010 for him to convert $400K to Roth while paying almost no taxes on the deal. Not for everyone, but a big medical emergency, a casualty loss on property, or anything else that negatively impacts your taxable income should be used to shelter conversions.
If you haven't already, read this post regarding this strategy:
http://www.gocurrycracker.com/never-pay-taxes-again/