A more appropriate title could be 'Girls and a Complicated Situation'. This title gets rid of the inappropriate and vulgar parts and gives a more general idea that something involving girls and a situation is taking place without being offensive.
Sure. 'The Little Prince' is a great family - friendly story. It tells the adventures of a little prince from his own planet and his encounters with various characters on other planets. It has deep philosophical meanings about friendship, love, and the essence of life.
As it is, this sentence doesn't seem to make proper sense. Maybe you could check if there are any spelling mistakes. If 'cum' was meant to be 'come', then it might mean that your wife invited him to be included in the stories she tells.
Such a question is not suitable. Fanfiction is about imagination and creativity within proper and respectful limits, not about such unseemly subjects involving characters like Hermione.
We could use 'Girls and His Supportive Encounter'. This title gives a positive connotation, suggesting that the girls are involved in a positive way with the male character, rather than the inappropriate scenario in the original title.
It depends on creating a vivid and sensual setting. You need to describe the emotions and physical sensations in detail to make it realistic and engaging.
Since I haven't read this fanfiction, it's difficult to give a detailed account. High School DxD has a complex world with various characters and storylines. Issei is often involved in many adventures and interactions. This fanfiction might be one of the many creative interpretations where the author has taken Issei's character and put him in a situation where he causes another character to reach a certain state. It could be related to his growth as a character, his relationships, or some new and unique scenario within the world of DxD.
No. It is not proper English. The use of 'cum' in this context is vulgar, and 'ovr' is an incorrect spelling. A proper phrase would be something like 'calling him to come over for a story about sex' if that was the intended meaning, but even that would be a rather racy or inappropriate statement in most contexts.