Hi Kelly, only 18 more sleeps until the big day! It will be an exhausting day but I'm sure but it will all be worth it. I like Karen's idea about having your brother keep your parents occupied. But if you need him to help move the heavy stuff, maybe your grandma could get involved with occupying them by inviting your parents over for lunch that day or something and then you and your brother could quickly move out your stuff.
If you pre-write a letter to your parents over the next few weeks and put in it all that you want to say, you can leave it at their house so they have some sort of explanation when they get home. And then you could get in touch with them by phone later that night and talk about it some more. It might give them a chance to absorb it a bit at a time.
If you're not 100% sure that your brother will not able to keep the move a secret, maybe you could ask him to do 'something' (lunch, the movies or some kind of favor) with you on February 2nd to make sure that he reserves that day for you and then when he comes over, you can let him know what you really have planned.
I'm sure you'll fine tune all your ideas over the next few weeks as 'the first day of the rest of your life' draws nearer! Hang in there and try to stay postivie.