This is quite normal.

Take the example of the paper tree. When you create your family tree, you usually focus on your parents, your wife, your children but in-laws come later as a secondary family of sorts. 

And this is a Famicity functionality that will be very interesting because everyone will have his or her own family tree. To see your in-laws, simply double-click on the box of your wife!

You will have a view of his own family tree and you will see your in-laws appear.

It is by double-clicking on the boxes that you will be able to navigate through the different trees of each.