personally, i thought the interview was an absolute **** show, but i still picked illinois. they couldn't fit everyone into the room for the information sessions. it was absolutely packed with little to no standing room, making it very hard to even hear/see anything. crowds stress me out, so i opted out of the tours and all of that good stuff. it kinda unnerved me seeing 300 people who i was directly competing with so i just chose to sit and read to take my mind off of it. fortunately i had already been on a private tour on my own so I didn't miss out, but friends who took it told me that it was once again very hard to hear/see. however, the actual interview itself was very nice and low stress.
my advice is to do as much research about illinois on your own because you won't learn much on the interview day if its anything like it was last year. the interview was one of the only things that really turned me off of illinois. previous interviews had made me feel like THEY wanted ME, but having 300 people at once made it feel like you were just another person. my parents came with as well and had such a terrible experience that they were not exactly thrilled when i chose illinois. while you may have a completely different experience than me, don't let the interview deter you. illinois is a great program! like i said, i highly recommend doing your own research and talking to current students.
also, yes, if you are invited to interview, then you will either be wait listed or accepted.