The terms of your grandson's probation will require him to notify his probation officer of this arrest within 24 business hours of being released from custody. Failing to do that would represent a second violation of his probation (being charged with another criminal offense would be the first violation) and make it much more likely that he would have his probation revoked and be ordered to serve time in jail.
If there is a conviction for the DUI in Illinois, that record would be certified by the Illinois Secretary of State to the Indiana Bureau of Motor Vehicles, which would then impose an additional license suspension of 180-365 days. He needs to notify his probation officer and hire an Illinois DUI attorney IMMEDIATELY.
You don't fully understand. Your grandson is charged with at least TWO Misdemeanors in Illinois (perhaps 3) Assuming he has an Indiana Driver's License, this is what he is facing in Illinois:
1.) DUI
2.) Driving While Suspended - Prior Offense
3.) Driving without Insurance
AND in Indiana:
1.) Probation Violation (at a minimum)
Your grandson needs a traffic / DUI attorney in Illinois AND a traffic attorney in Indiana. This is EXTREMELY serious. Accumulating 3 major offenses (e.g. DUI, Driving While Suspended, Reckless Driving) in 10 years gets you classified as an Habitual Traffic Violator (HTV) and can result in the loss of driving privileges for a MINIMUM of 5 YEARS.
This is NOT to be taken lightly. He would be best served by an attorney familiar with both Indiana and Illinois traffic law. Good luck.