Just saying, sibling-coded is NOT a valid argument against a ship. If you PERSONALLY think they're like siblings, that's YOUR headcanon. Nobody else has to go by YOUR headcanon.
KNUCKLES AND AMY ARE NOT SIBLINGS. KNUXAMY IS PERFECTLY OKAY.
However, if two characters CANONICALLY view each other as siblings despite being unrelated, that is PSEUDO-INCEST. When it comes to that, it's a slippery slope on morality.
LUZ AND HUNTER ARE NOT SIBLINGS. LUNTER IS PERFECTLY OKAY.
If two characters are biologically related or are adoptive siblings (includes being raised together as siblings), that is INCEST. Incest is BAD.
SONIA AND MANIC ARE RELATED. MANIA IS NOT OKAY.
(Edit: Removed Shadria, as they are not canonically siblings. Shadria fans should still DNI, though.)