If you were arrested and a complaint was made, then most likely you will be charged. The time to speak to a lawyer is now, before the charges have been filed. This will give your attorney time to sit down with you, review the situation, and try to work to resolve the situation before it escalates or worsens.
The State can choose either to prove that you were under the influence of alcohol and it impaired your driving or that your BAC was .08 or greater while you were driving. It is doubtful that you will go to jail, but a good attorney can explain your options and the likely outcomes of your case. Most attorneys, including many of the ones listed here, offer free consultations. You should speak to one as soon as possible.
Unfortunately, your PO doesn't necessarily have sole discretion about whether your probation is revoked. It's a good instinct to try to retain counsel at this point in time. Try Avvo's Find a Lawyer feature or search for attorneys in your area.
On the most serious charge (aggravated DUI resulting in death) your brother faces 1-12 years (assuming only one fatality). He will not be eligible for good time credit, meaning he will serve 85% of his sentence, and probation will not be available unless the judge finds very special circumstances. He needs to hire a very good defense attorney immediately.
The possible criminal charge is Leaving the Scene of an Accident. Leaving the Scene of an accident is a Class A misdemeanor and carries up to 1 year in jail and a fine of up to $2500. Conviction also carries a possible license suspension depending on the amount of damage to the other vehicle. Consider hiring an attorney, especially if you receive a ticket in the mail.
If you hire an attorney? Very small. If you don't? None. These are fairly serious charges, and there are several of them. They could have long term consequences for your license, your driving record and your criminal record. An attorney can help you minimize those consequences.
Contact an attorney who practices in Kankakee (or wherever the ticket was written). I used to live there, and most defense attorneys offer free consultations. They can give you an idea of the charges you are facing and the potential consequences.