Thanks for the ask!
I’m always happy to answer questions about little-talked about fankids!
Unfortunately, Sirius and Regulus aren’t super developed yet in terms of goals, relationships, etc. I can definitely share my ideas and inspiration for them though!
These two are identical twins and the little brothers of Hymnia. They’re actually her half-brothers, born about six months after Grimsley and Shauntal’s wedding (a wedding that may have been moved up a month or two to accommodate Shauntal discovering the pregnancy). In terms of looks, they inherit Shauntal’s dark purple hair and Grimsley’s light blue eyes. Their hair texture is closer to Shauntal’s as well and doesn’t spike up the way their father’s and sister’s does.
Sirius is the older twin and is quite outgoing and headstrong. He inherits Grimsley’s skills for being sneaky and getting into trouble and is very stubborn. He’s the type of person who’s good at manipulating others, but he’s not especially mean-spirited or anything. Compared to Hymnia, he’s an angel (well, most people are to be honest). Regulus is the younger twin and is on the sickly side, in somewhat a similar boat to Wally. Similarly to Wally, he gets better as he gets older, but he was stuck inside a lot as a child. As a result, he’s a bit more subdued than his brother, but no less devious. He figured out early on that being the “sickly child” meant adults would dote on him. Regulus gets along pretty well with Hymnia, while she and Sirius tend to argue and fight. She’s very protective of them, however, and they’re some of the only people she truly cares about.
In-universe, I like to imagine that Shauntal decided to reread the pokémon world equivalent of the Harry Potter series and was inspired to name them Sirius and Regulus as a result. The names sounded dignified and regal enough to suit Grimsley’s tastes, so they stuck!
Out of universe, my reasoning for the names was as a reference to the characters these twins are (fairly loosely) inspired by. The reasoning involves some spoilers for the Black Butler series (albeit ones a year or something like that old), so I’ll put it under a cut!
I’m not sure when this started, but somehow I got it into my head that Grimsley reminded me a bit of Vincent Phantomhive, so I thought it would be amusing if Grimsley had a son that resembled Ciel. This is the entire basis of the twins – I’m not joking. The fact that they’re twins is the spoiler, though I’m not sure it really counts as one anymore. Better safe than sorry and this answer was getting long already!
The name Sirius came from the fact that Ciel’s brother (the real Ciel) went by that alias in the manga. Then choosing Regulus for his brother was actually inspired by Harry Potter, as it was the name that first came to mind as a “paired name” with Sirius for me.
As such, you can picture the twins as looking like Ciel with a different color palette. Unlike their inspirations, however, they don’t really get any angst and live happy lives! That said… I do have an AU featuring Regulus and Hymnia as the primary characters that’s closer to Black Butler canon. This post would really get too long if I talk about it in detail though, so I’ll save it for another time!