Although there is no specific forum for you and your site members to write on, you and your family can write messages in the newsfeed, and the whole family will see.
The newsfeed is not a substitute for forums. Under activities content, it indiciated that you can choose to have forums on your site. When will that feature be added?
I am sorry for your inconvinience, but the activities pages are currently not available on our site. (You still can view the articles, which you've added to your site a few months ago, but can't add any new activities)
We currently don't support thos pages, as we are working on improving and developing various features for the family site, and we'll let our users know, once we'll release new features for MyHeritage.com site.