A friend and I found this recently and have been hoping to play but have been struggling as it's not a particularly intuitive process. We've been trying every guide we can find and most of them say the same thing but it doesn't quite work.
So far we've been able to get our KIs and add each other as buddies. We've been able to get into each other's Relto and we've both finished the Cleft. We can get into one of the next ages together by both visiting one of our Relto and then using the bookshelf - but that is quite cumbersome and the invite process that lots of links describe seems a lot better.
When we send an invite to the age visitor list then it is received but it doesn't show up in the Private Links - not sure why.
Also, when we were in one of the ages we found a cloth that teleported us somewhere else that we couldn't just go back from - it didn't seem to be part of the level - was wondering what that was about?