What is the ruling on an adult, skilled wife playing with her sister's husband, even if it happens by chance only once, in front of relatives, and for the purpose of pleasing the children and joking?

The husband of a woman's sister is a stranger to her, so it is not permissible for her to play with him, because it is a means to temptation, and the Shari'ah came to block the means [to evil]. The Sunnah clarified the grave temptation of women, for the Prophet, peace and blessings be upon him, said: "I have not left behind me any temptation more harmful to men than women." He also said: "Beware of the world and beware of women, for the first temptation of the Children of Israel was concerning women." Therefore, caution is obligatory, and one must avoid the pitfalls of Satan, for he gradually lures a person into temptations. Allah Almighty says: "O you who have believed, do not follow the footsteps of Satan. And whoever follows the footsteps of Satan - indeed, he enjoins immorality and wrongdoing."