With only six people, why not simply create an email list like on Yahoo or something and have everyone who writes email the list that they’ve done so? Or simply expect that all six will check the blog at least daily? That’s what I would suggest. If they can’t be bothered to do that, how committed can they be?
As I said in the other thread, if RSS feeds were available for private blogs, anyone could subscribe to the feed and read the entire blog. I doubt there’s a platform out there that allows this, and if there is one, it’s obviously fundamentally flawed. It would not be private at all.