......A good analogy will best explain the relationship between groups and families. Let's take three different musical instruments. For our purpose, we will refer to each musical instrument as a "group". Group one will be piano, group two will be a violin, and group three will be drums.
......Why musical instruments? Well, as you well know, a single musical instrument is capable of generating different sounds at different frequencies. If that was not the case, the music world would not be quite as colorful as it is today. If we look at three different frequencies for the musical instruments above, we can generate at least three different kind of sounds for each of them. If you use the extreme and mid frequencies, we will have a low tone (deep sound), medium tone, and high tone (a squeaky sound). Let's refer to the musical instruments as "groups" and the tones as "families" to fit our purpose...