Should my husband be spending the same amount on all our kids

My husband has a son with his ex wife and we have 4 kids together. His son lives in a little apartment and is on disability for his autism. He has a caseworker who checks up on him weekly along with a service dog but he has trouble keeping his home clean. So my husband and his ex wife switch off every week on who's paying for the housekeeper which is $112 dollars. I think if he's gonna be spending that money on his adult child than he needs to spend the exact same on the minor children we have now. He asked what do they need the money for and I said to keep it fair and he said "Well life isn't fair." And that I'm more than welcome to use my paycheck to give the kids $112 each but he's not doing it just so everyone feels equal. I want all our kids to be treated equal. If he's gonna spend the money on one kid, why can't he do it for ours?