My husband and I are having our first child. He pays a lot of child support for his son who he only sees on weekends. The mother is remarried and they now a child together. We are barely getting by when it seems they are doing well. I live in CA so the child support laws are strict. I want to find out how to reduce cost of child support each month with the above scenario.

The only way he can get out of paying is if his ex's husband wants to adopt.
You can go back to court and get the order modified if there is a decrease in income
Those are the only two ways I know

He can file in court for a modification of support based on the fact that he has another child. That is a large change, however, it probably won't drop it by that much because the other child was born first (and he knew he had another child to support before the two of you decided to have children). I'm not judging but that is the way the law looks at it. If he has had a significant decrease in income that would also be a factor. But no matter what it means going back to court.