you are able claim your brother in laws (as well as your MIL
I don't know this for a fact, but I would expect it "might" have the potential to affect the amount of child support (and any other support) received. Especially if challenged by the payer of such support. I would suggest you check with qualified legal authority licensed to practice in your state. Especially if the state also taxes personal income and you would be reporting those dependents on a state tax return.
