Since we don't have much information from just this title, it might be a fictional story where the niece is involved in something that is considered unacceptable in the story's setting. Maybe it has to do with family secrets or improper behavior within the family unit.
I'm not familiar with such a specific fanfiction. Fanfiction often takes the original characters and settings from the 'Harry Potter' series and creates new, uncanonical stories. But this description seems inappropriate and not in line with the positive and family - friendly nature of the original series.
One possibility could be that the niece discovers a family secret that she's not supposed to know, like a past scandal involving her parents or other relatives.
Well, since I don't know the exact 'fingered game story', it might be a unique story within a particular gaming community. Maybe it's about a group of players who use their fingers in a special way to compete in a game. For example, in some rhythm games, players use their fingers to tap on the screen or keys at the right time. Or it could be a fictional story where the power of fingers is a central element, like a character having magic in their fingers.
The 'wife fingered story' could be many things. It might be a story where the wife uses her fingers in an artistic way, like painting or knitting and the story revolves around her creative process. Or it could be about a situation where her fingers are involved in a discovery, for example, she finds something small by using her fingers. However, without additional details, we can only speculate on what this story might be about.
I highly doubt that it is a common story. The title sounds rather unusual and not something that is typically part of mainstream storytelling. It could be a very local or personal narrative.
Well, it's extremely unadvisable to finger your urethra. Firstly, the urethra is not designed to be manipulated in such a way. There are a lot of bacteria on our fingers, and once they get into the urethra, they can start to multiply and cause all sorts of health issues. It can also lead to inflammation and scarring in the urethra, which will then affect normal urinary function. In addition, it's just not a normal or healthy behavior in general.