Wow, you leave tomorrow! Good luck!
Well, my two cents worth on this - you might be surprised how much you change your mind about things, even when you are certain about how you think you will respond... well, never underestimate the unpredictability of your emotions and the events that play on them.
Were I to be in your position, I would ask them to wait until the transition process for you was complete (and you could tantalize them with this by saying you will be able to help them when the time comes because you will have the experience, etc...) Unfortunately, there may not be much you can say that won't hurt them, so instead of saying don't, or wait til I want you, perhaps try an angle of "wait until I can help you". If they argue that they are ok without your help, you might point out that it would be a difficult for you because you would feel a sense of responsibility for them, and you would want to be able to help them.
I am assuming on the emotions a bit, but this might be a way to solve the dilemma without too much emotional distress? Like everyone else said though, they could visit and decide it's too much of a change, or the time and effort it would take to accomplish it could get the idea out of their minds.
Good luck though with everything, and congrats on your wedding.
Tmac