A group allows you to group your family under one heading (eg, "My family"). This will allow you to share with your loved ones m...

To create a group, you must go to the "My Groups" tab from your space "My family". Once on this tab, click "Create a ...

To add a person to a group, click the group you want to add your loved one. On the right side, click "Edit Group". ...

To remove someone from a group, click the group that you want to delete relatives from. On the right side, click "Edit Group". ...

By default, the group "My Family" consists of all the people on your tree.

By default, your in-law family consists of the entire family of your spouse and their parents and other family..

In general, when you write or share with your in-laws only, it is logical that your children and your wife have access to this album or this story. ...

No that is not possible. 

You can add the same person to as many group as you like.

To see those present in your group, simply click on the group. On the right side you will see the list of people in the group.