Agree. Either Blogger.com or
Wordpress.com. They are the two of the longest running & successful free bloggers' sites. Free Wordpress.
com should not be confused with Wordpress.
org which is their paid side of the site, for professional bloggers.
It just depends on the different features and free templates you want to choose from. What's nice about Wordpress is that they have a text box format, similar to the one the DIS uses when you create a post. No needing to learn any fancy webpage coding. Blogger.com is a little different. I think they also have more free templates to choose from.
You can set up each with privacy settings, allowing only the 3 of you to add content, and also limit the amount of people who will actually see it.
Both have no intrusive or annoying ads you have to have just to have a free blog. Wordpress just adds a single line at the bottom of each webpage. And you can change the size of the font for it to make it small. I think it's a fair trade for a free blog.
Sign up for both, then play around with the sites & templates and make up some test practice posts. You don't have to publish anything. And you can keep the blogs totally private as the three of you play around, figuring which you like better. You can rename the blog, and also delete any posts or the whole blog at any time.