I've done that when making me and my cousin as Sim's but it's just kind of pointless and too much of a hassle you know. I think it would be much simpler to have an elder and a child to just be labeled as grandparents, without having to add the parents, adding cousins without adding, two adult-elder siblings, and parents.
You know, I think it would be helpful if The Sims 3 Launcher provided us with an Adware/Norta-Track type of feature, that would scan any third party CC, as well as "modifications," as well as the backup files, found in the DC Backup folder. Any third party content that the launcher detects as harmful, would automatically be safely removed from the game, along with the DC Backup files. Anytime you download anything from the exchange, the launcher would scan, detect and safely remove the corrupted CC. Also give you a pop-up message "the following items were detected as harmful, and safely removed from your game." Provided with a list of those harmful third party items, that were considered harmful, and therefore removed.