User blog comment:B214/Volume 22 spoilers/@comment-24593185-20160722022934/@comment-1359322-20160723103324

You do realize that a new set of Satan is being chosen right now. So Sirzechs is no longer a Lucifer.

Even before that, Millicas is Sirzechs' son. In your own damn words, he would be a son of a ruler but  Millicas is still a Gremory not a Lucifer . So no Sirzech's being a Lucifer doesn't make his wife a Lucifer. The story stated clearly, the current title of the Satan are akin to President of the USA. The position can be replaced by someone else.

In this case, Sirzechs is the one chosen to take the spot of Lucifer, not his family. The same applies to all other Satans, their family don't hold the title of Satan whether its the wife or even the kids.