[quote=@FrogRFlowR]
Oh yeaaaah but they cannot be born right? Cause its only women?
[/quote]

I'm not sure about the previous system but under the current system, they can indeed be born from a monster-human couple.

[quote=@FrogRFlowR]
I read some people write about clans and families, I am/was under the impression it was monster girls families. So if I want to play something more like a devil, succubus or any other half animals monster girls, they either were humans before or formed from mana? 
[/quote]

Well, Succubi and Devils aren't exactly half-animals. They are monsters through and through, just like how a Holstaur or a Minotaur isn't a cow turned into a monster.

If you want to play as a Succubus, she can be as you said: a human girl turning into a monster. Alternatively, she could be a child of a Succubus-human couple or a Succubus from before The Great Change, that is she would be over a thousand years old.