Whoever it is that keeps on changing the parent, stop it. It has always been that Pixiv pics are to be prioritized over Twitter ones.
It is standard.
No, that's not how we do things. Pixiv took priority in most situations before because Twitter sources were almost always lower quality because of Twitter's harsh image compression. Twitter doesn't do that anymore, Twitter images are often identical to their Pixiv counterparts.
Parent priority goes to the better quality version, and in the case of two images of identical quality, then the one uploaded first is the parent.
This post is a pixel-perfect duplicate of the parent, meaning it should be the child. It keeps being changed by the bot of an Admin that detects duplicates, which will keep changing it no matter how many times you change it back.