So basically I changed the whole 'Yin and Yang' thing
Yan is hellucard since he's more a good person and wouldn't really harm anyone. If you can't pay him, he doesn't do something horrible, he just does something small that only goes for a day. He does use some magic which was under his sleeve but they aren't normally bad. It's just showing other's pasts, tracking everyone around him and having a very good hearing ability. He can also sense emotions. The only cons are that he normally defends Ying, even if he's hurt hellucard way before. Another con is that he actually can't run after anyone when tracking. He isn't good at running, even if his sign is that he's active, he doesn't use this often. He doesn't even go out to run.

Ying is Yuu, since he's basically possessed for one and that he's worse. If you don't pay him, you HAVE to make a deal with him or, in at least 30 minutes sharp, you must bring the payment. Otherwise you're fucked. He uses magic as well but it's more dark. He can cause really bad hallucinating just so they'd suffer, he could deform a specific part of the body and it'd have to be hidden otherwise some consequences will come with it. He could basically cut your entire body in half by a simple scratch. But that's only because of him being part demon. If he wasn't, he'd be a weak boy. He can also track people but he has incredibly great sight, so he could probably see someone from miles away but still know who it is. Con is that he's not THAT reliable for good things, like where the killers are and who they are and how to get them. You're asking for trouble if you do. But he's great at actually getting the killers away from trouble.

Hellucard Yan is basically gonna be hidden from the cops, for a while, before they find him and demand answers.
The cops will more likely go to Yuu Ying first because they think he'd probably try to help. Which is a lie.

The reason they're basically a copy of Yin and Yang is because that title was basically stolen from Yuu and he just calls hellucard that since hellucard isn't well known upon everyone. He just changed it so people could sorta be confused since in that town, no one really has knowledge of Yin and Yang either because of them not caring or them being dead.