Parental information for FAFSA

I am an independent student but my brother is not.

He will be using our father to fill out parental information. Our father is illegally married to his cousin. Their marriage is not recognized by our state. Will he need to include the cousin’s/“step parent” information?

Do they file a joint federal tax return? If so, they are married for FAFSA. If not, they are two people living together.