"Big Sister Twilight" and "Big Brother Spike" Tag

Hello.
 
I am looking for approval from moderators for certain tags that would be added for certain artwork and/or images, specifically images involving Spike and Twilight’s relationship. I know there are those who view Twilight as a motherly figure to Spike and I know there are those who view Twilight and Spike’s relationship as that of a brother and sister.
 
As a result, I am seeking approval from mods for these tags especially the “big sister twilight tag with the addition of the “big brother spike tag should there be images of their roles reversed not just to make it official but to also appease those who view Spike and Twilight’s relationship differently and perhaps to balance things out.
 
I appreciate any feedback from non-mods as well if those who are on the same page and see them as siblings as well.

@LightningLazer
 
I was ready to argue that mama twilight already covers this, but it actually seems to refer to any situation where Twilight is a mother, not just to Spike.
 
First, if big sister Twilight has to be a thing, it should imply mama Twilight.
 
Second, big brother spike sounds like a good tag for the specific situation where he’s the elder sibling. I would just add that it should also imply role reversal.