It is time to be a business man w.w., you have to take the site down until they pay you. It is as simple as that. If the fact that they are not paying you is not making you upset, just think about your kids and christmas. Now if that does not upset you enough to do it, imagine them taking food from your kids and them starving, because that is what is happening in a sense.
It is a dog eat dog world. I know that is not fair and people should not be like that, but for the most part that is the way that it is. Also, once you give someone like that an inch they will take a mile.
Your family should come first above all, including your feelings about this. Just block those out.
What you need to do in a civil manner is call them and tell them that you were told you would be paid the full amount when the job was complete, which was 12/14/2010, if I read this thread right. You will give them 24 hours to make the payment and if it is not paid then the site goes down. Stick to your guns.
On an ending note, really thinking about them being family friends. If those are family friends I really hope you have no family enemies.
Good luck and Merry Christmas