What happens in child support court? kinda long

My brother and his childrens mother went to a hearing for child support today. They ask you to bring proof of income and all that kinda stuff. She came in with a paper that had the general salary for her position, not a paystub. She works at citifinancial so she gets lots of bonuses during the year. Over the last 2years she has made over $45,000. However, the paper said the job pays 35,000. She also told the lady she pays 1500 for child care each month but didn't have any documentation from the daycare, this was just word of mouth from her and the lady typed it into the computer without asking for proof. my brother refused the amount that they presented him to pay because she withheld info which made his payment higher. He takes care of his kids and wants to continue to but he also wants it to be fair. Because he refused the amount, they have to go to court and be heard by a judge.
What should he expect when he goes? Are witnesses allowed? what kind of info are they going to ask for? And is the judge going to except ehat she says or require her to show proof of any expenses that she says she's paying out.

Your brother really NEEDS an attorney for this one! The attorney can subpoena her bank records, her boss to testify, the daycare people and their records.
I had a similar experience a few years back, my ex was claiming she made poverty wages and flat out refused to bring in her documentation. Out of the blue she bought a house nearby so I hired an attorney and told him to subpoena the mortgage company records.....turns out she made 60K a year, put 21K down on the house.
The judge was so angry he turned the case over to the local sheriff for perjury, she was found guilty and spent 15 days in jail.....and the support was adjusted accordingly. It cost me a 500 retainer, she had to pay that, plus the judge ordered her to pay the attorney for the time he had involved in the case.
So make sure he gets an attorney!!!!!