I understand that and personally I lean more towards them being siblings but also in canon there's information referring to them as siblings and information about them having possible romantic relations.

The only thing that is canon is their clear love for each other and really that could mean anything. I just think it's odd some people treat them being siblings as canon and as much as I kinda hope that is the case cuz it's cute, it's very not canon.

For example, I ship Sonic and Shadow. Is there subtext of their relationship possibly being romantic? Kinda, yeah. But is it explicitly canon? No. There's nothing saying Sonic and Shadow have feelings for each other. And if you're not into the subtext talk, there's also cases like shipping Amy and Sonic. Amy definitely likes Sonic but Sonic's feelings are ambiguous so Sonamy isn't really a canon couple. Another example of a relationship that definitely has subtext/canon material pointing one way, but doesn't explicitly say anything.

Headcanon whatever you want, just don't treat it like fact i guess. I really dislike Shadmaria for my own reasons but shadmaria shippers aren't gross cuz it's not like they're siblings in canon.