Okay, this isn't doable.

Now, changing the interface to show only the listings you want to see is doable, but the block chain is open to being looked at by everyone.

There is nothing hidden. It would take immense effort to hide it.

meaning, you would have to encrypt every post and then only decrypt the post for all the people "authorized" to view it.

So, most people just view their feed. And that is a list of people they follow. But, the bots and anyone who wants to, looks at the entire block chain. And everything is visible.