What is right for your children and what is right for them by the law are 2 distinctly different things.
I assume your wife is aware of your situation. Come to an understanding with her as to child support. Tell her you will be truthful and provide all documentation as to what you make and that you will give a percentage (that you both agree on). For instance if you make 40K this year you will give 30%. If next year you make 80K then you will still give 30%. Look at what you have spent on the kids in past years and figure out how much that was as a percentage. Add some due to the fact that kids get more expensive as they get older. Provide for college.
That is just my advice. My belief is if you start looking at those child support calculators then your attitude is that you are trying to get out by paying the very minimum for your children. That is doing them a great disservice.