Curate, connect, and discover
I've seen a lot of posts saying that the Sparda boys are living heaters, but I feel like that doesn't quite make sense. No, I raise you. I think they run cold, hear me out.
I know that Makai/the demon world has multiple biomes, but we know at least one of them, the one that we play through in the game, is the fire hell. It would stand to reason that the Sparda boys would have a lower internal temperature and or be cold blooded to compensate for how damn hot it is. Also, their demon forms appear very reptilian. Of course, things work different in the demon world, but it could be safe to assume, that like reptiles, they could be cold blooded, which would mean in a cooler environment (like earth) they would be a lot colder. This is backed up by the fact that you almost always see the Sparda boys wearing their big ass coats. Nero even double layers a hoodie with his coat in dmc4, and they all keep their coats on regardless of season. In dmc5, Nero has a shirt and a sweater on underneath the coat.
Maybe I'm crazy, maybe I'm overthinking it, but I think the Sparda boys are quite icy in the human world. And maybe I'm just biased since I like the cold better, but I feel like I'm onto something.
P.S. V is not included since he's just straight up human, and also I wrote this while a little bit high 👍