Except as I've already told you, IT'S REDUNDANT. We already have the Siblings category, and that by itself should be sufficient. Add that category again and I will be forced to call in one of the mods.
Continuing from the above I've yet to see you send any kind of message to any administrator. And honestly you really shouldn't bother because you frankly do not have a case. The "Sisters" category is redundant and unnecessary in light of the "Siblings" category. Ergo, there is no good reason to have both and thus I was not in the wrong to remove the Sisters category. You may not agree but it's pretty clear as day to me.