How do they factor in 2 kids from a prior marriage when figuring child support?

Depends a lot on what state you're in, whether you or your ex-husband has custody of the kids, and whether the mother of the 2 kids from the first marriage is still in the picture.

In some states (like here in California) there is a computer program that you input a lot of financial, custodial, and property information into, and it spits out a number and the judge then considers that number in light of the global circumstances.

In almost every state, if you and your ex-husband can reach an agreement betweent the two of you that you both can live with, the court will approve and enforce that agreement. If you do reach an agreement with your ex-husband, WRITE IT DOWN and make sure that BOTH OF YOU SIGN IT. Both of you get a copy.

Yes, they will take the other two into consideration, just as they would if they lived outside of his home. They don't want to feed your children while starving the others because they just happen to live with him. That and because of the situation the judge is likely to handle it far different then what any calculator will give you. My guess would be he will pay give or take 10% of his monthly income to you in child support.