Just an fyi, this is from UIUC’s website:
“If you are a dependent: Your family must live in or move to Illinois for at least 12 consecutive months immediately preceding the first day of classes. The in-state tuition rate would begin at the start of the next term.
If you are not a dependent: You must live in Illinois for one full year for non-educational purposes. This means that during that 12-month period, you may not enroll at any institution of higher education more than half-time.”
Is your family moving to Illinois. Buying a second home would not qualify for in state tuition.