No. Like porygonlord and I said before, a pure family has two eggs. Sometimes if you get a pure family (let's use the Mame Family as an example) and you marry the Mametchi to a Chantotchi again, hoping to get another generation of Mame Family, you won't. Instead you'll get a Smart Family, which is a step-down from the Mame Family. Also, the Violetchi will turn into a Mamametchi.
To check to see if you have a pure family, check your family's status. If it says "Mame Family," "Violet Family," "Kuchipa Family," or "Meme Family," you've got a pure family. Also, when the babies of a pure family evolve, one of them will be an adult and the other a teen. You can use that as a pure family reference as well.