I've still got a lot to figure out but I've been making some demon lore! At the moment the two biggest plot points are demon's last names and how breeding between them affects their temperment.
A demon's last name is usually tied to how they act and what powers they have. The 7 deadly sins are the oldest and most powerful demon families while spin offs of those belong to everyone else. My oc Danica's last name is Tristis which (should be) depression translated from Latin. This means her family gives off a depressing aura and are in a constant state of melancholy. The affect of their last name could be canceled out by other demon blood, but her family has lived in the human realm for a long time and they haven't bred with other demons. Human blood dilutes demon blood at a much slower rate than other demon blood. In Danica's case, this means while the rest of her family are mostly unbothered by feeling so numb and sad all the time, Danica wishes she could feel happy and fit in. Her demon qualities from Trisits have lost some affect which makes Danica more aware of how she feels compared to the rest of her family (if that makes sense).
Other demons like Hobart, have lived in Hell all their lives and have blood from all kinds of demon families. Because of this, his last name Inprobus, which means rebel, doesn't make him behave the name would suggest. Demons have longer life spans than humans and so their blood isn't diluted so fast since most demons are irresponsible and have a hard time raising an offspring to adulthood. There are demons who are more human like in nature and can be responsible parents and even citizens. These demons usually try to escape to the human realm, where they are faced with prejudice for being demons. For the moment the reason demons can even live with humans is because, the agreement between demons and humans happened recently in an event similar to the Civil Rights movement. (I haven't thought a lot about that part yet)
Haha I hope this made some kind of sense! I've been having a lot of fun with this lore for demons and my next step is to tackle angels!