I always think in families like tags or classes that you can give to objects to "group" and reference them in events. In reality is something more complex than that, but in essence it's really close.
On the other hand Containers in CC are something more related to the concept of "parenting" than "grouping", because an object can only be contained by another object that already exists. In "grouping" a collective of objects create a new entity that is a group.
In this sense I think Families are more related to grouping than Containers. Although in CC both only "group" objects in the runtime not in the "edit-time".
Would be a great addition to C2 if you could group objects in the layout editor as well. If you ever used a vector editor you will understand how useful this would be to Construct in helping manage layout content, and extending this concept with the ability to reference and manipulate them through events would make it a very powerful feature.
I really expect that the families/containers/groups/classes/tags (or whatever you prefer to call it) be well thought with a lot of care and respect for C2, since they perform a fundamental role and yet have very similar concepts and overlapping functionality.