How can I separate posts to my wife's relatives from posts to mine?

[pri✍]

So you want to post things that only your family to see and post things that only your wife's family to see, right?

First go to your FRIENDS in your Newsfeed, then click Create List, name it My Family (or anything you like) and put all your family in there.
Next create another list, say Wife's Family and put all your family in there.
In the meantime, I think you already have Family list (created by FB) that you put your family & your wife's family in there.

Now if you want to post something that only your family who are able to see it, before you press Post, click the audience icon (globe for Public, etc), click My Family.

Remember, that audience setting is remain the same for future post until you change it!

So, if you want to post something that only your wife's family to see it, change that audience to Wife's Family among the options listed in the pop-up when you click the audience icon.

I think you got the idea when you want to send Christmas greetings to both sides of family.

As you got the idea how to do that, you can make other friend lists that suit your need.

Good luck.