What are the limits of interaction with a sister's husband by suckling who is characterized by bad manners and who spies on people's private matters by looking, and what is the ruling on his staying overnight with his wife's grandmother who lives with her daughters without a mahram, and what is the ruling on his sleeping next to his wife's aunt and kissing her head?

The husband of a sister through suckling is a stranger to her sister, both by suckling and by blood, and should be treated as such. Similarly, the wife's maternal aunt is a stranger to her niece's husband; therefore, it is not permissible for him to kiss her head, shake her hand, be alone with her, or sleep next to her. Moreover, following one gaze with another is forbidden, as Allah Almighty says: "Tell the believing men to reduce [some] of their vision and guard their private parts." And the Prophet, peace be upon him, said: "Do not follow a glance with another, for the first is permissible for you, but not the second." This man should be advised, and the Shar'i ruling should be explained to him, while also being cautious of him and keeping a distance if he is ill-mannered and does not adhere to the Sharia in his gaze and actions. As for his sleeping with his wife at her grandmother's house, where there are daughters, there is no harm in it as long as it does not lead to a Shar'i prohibition such as gazing or seclusion.