Ruling Family, in the context of the Towns of Cygnus, refers to a Town's royal family as a whole. Most likely this is limited to only the immediate family that preceds over a town, and not relatives eg cousins, aunts, etc unless they are given some sort of offical position. Most ruling families at least have a King and Queen, though sometimes there are towns that are an exception to this, such as Webberton which has only a Queen and a Princess. Chris Corners is something of a rare exception as there is not only one member of the Ruling Family, The Boss, but they are also male as well.
Ruling Families tend to follow a single blood line, with the current rulers' children taking over the town, or marrying over into other towns' royalty. Though should anything happen to the current rulers, a new ruling family will be elected.