LJ-
Jennifer & Anne speak from experience; just do it.
I've been telling my family I'm moving to England since I was a little kid. Now that I've got an actual, solid plan to move over (uni. in January) they're still treating the announcement as if it's coming from a little girl (I may be the youngest, but I'm 37 for pete's sake!).
If moving to England is what it takes to make you happy (as it is in my case), you HAVE TO make that clear to your family. Afterall, they love you and want to see you happy, don't they? If it's important to you, it should be important to them. And with the internet you're never too far away! Added selling point: most of my friends and siblings are thrilled that they'll have a place to stay (my floor!) and a tour guide when they come over!
Sell it. And don't be afraid.
Marybeth