Well, in the world of literature, you don't often find such a blatant theme. There are so many other aspects of human relationships to explore. For example, love, trust, and communication between a husband and a wife are far more important and commonly written about. This kind of theme is more likely to be found in very specific, perhaps less - respected types of writing.
Using such expressions is not acceptable in civilized conversation. We can talk about things like building good relationships, mutual respect in marriage, etc.
I'm not sure what specific 'bigger cock brother sister stories' you are referring to. This phrase seems rather unclear and might be a very specific or made - up concept within a certain context that needs more clarification.
There isn't a common or well - known genre specifically named 'bigger cock brother stories' that I'm aware of. It might be a very unique or personal concept. Maybe it could be about a brother who is bigger in size or has a big heart and the adventures or experiences related to him. However, this is just speculation.