Child support modification

I’m not sure where exactly to post this or if anyone can help. But here it goes! Lol. So my husband pays child support for my step son and we are seeking a modification. We now are married (we were not at the time the child support was set up), our living arrangement has changed (we were living with his mom at the time) and we now pay rent and all the bills that come along with being an adult lol (electric, water, cars, phones, etc), and we just had a baby in December. So with all this taken into account, we need to modify the child support. We live in FL if that makes a difference. We currently pay about $700 a month 😳. My question is, one of the questions on the paperwork asks how the modification is in the best interest of the child. I am not sure how exactly we need to answer this. I mean it is in the best interest of the overall family. My husband is the main provider. I hardly work and I haven’t been since having the baby. So with the new home & baby, I don’t see how we wouldn’t be entitled a reduction. But idk how to say it is in his sons best interest. Oh and I forgot to mention, custody is 50/50. So it isn’t like we just aren’t wanting to pay or anything. We have him half the time and I think $700 is crazy to pay when we have him just as much as her.