The first thing we noticed with TheFamilyPost.com is that it is entirely Flash based. This was fairly common several years ago, but full flash sites are no longer currently built due to the fact that they don't work at all on iPhone/iPad and have issues on other mobile/tablet devices.
The Family Post does not appear to be setup for collaboration between larger extnded families. It is more geared toward a family that wants to setup a public website to share photos, videos and stories with others. Per the demo site we used for our evaluation, all your content would be open to anyone on the web. However there may be controls to change this in the paid version. The Family Post does not offer a trial version of their software.