Unfair babymama?

So my husband lost his job recently. He's been looking for other jobs and has a few interviews lined up. Well currently im making all the money and I get paid very well. Enough that if my husband really wanted to he could stay home and watch our kids. Well he has a son from a previous relationship. She's completely insane it's ridiculous. So we have our two daughters in private schools. We pay around 3k a month for both of them. Well now Mommy wants him to enroll in a private school. I'm okay with it because it's their education however what I'm not okay with is that she doesn't want to go half and half. My husband isn't working and even if he did he doesn't think it's fair we take all the financial responsibility. He already pays for everything even after child support which is 2k a month. Our bills total up to $7800 a month currently and with my step son being added to a private school our bills would end up being $9800 close to $10k a month which now at that point we cannot afford. She never wants to take responsibility for her son. When she signed him up for football she didn't want to pay for the registration fee or equipment. We paid everything because this is something he really wanted to do and he's good at it. Honestly I'm just tired of her being a lazy parent. She doesn't want to work when she's capable of doing so but she wants to go on vacation all the time. Last time my step son was here he told my husband he wanted to move fully with us. I'd be more than happy for him to stay with us because he's better off here. I just don't know how she's going to act. We also asked him if he really wanted to change into a private school we would put him and just bust our asses off to afford for our kids education but he doesn't want to because all his friends go to the same school. And his public school isn't bad at all it's actually a high ranked one in our city. But mom just wants to push this private school thing so much because she's always trying to prove something she's not. I mean is it not fair for her to pay half and half?