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.
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.
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.
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.
A complaint is the formal method of charging any case. A DUI case may be brought either through a State's Attorney filing a complaint or by an officer writing a ticket. If the case is going to be upgraded, generally the State's Attorney will file a complaint that supersedes the ticket written by the officer.
You technically can, but I'd be cautious about it. If an officer stops you, he/she will likely go by the information they're receiving from the Secretary of State, and if the SoS says you're still suspended, the officer might write you up. If you want to be safe, wait for notification from the SoS, or call to confirm the suspension has been vacated.
It rarely hurts to have an attorney with you. Oftentimes a local attorney will be able to give you an idea of the quality of an offer made by the State, and he/she can help you understand the strength of the evidence against you. Some attorneys will handle cases like these for only a small fee, and most offer free consultations. Try calling some local criminal defense attorneys or using Avvo's Find a Lawyer feature.