What should I do about my wife who violates agreements regarding the upbringing and privacy of our children, allows her sister to sleep in the children's room, puts her sister's clothes in my bedroom, and might she also allow her teenage brothers to sleep there?

Our advice is that you come to an understanding with your wife, and remind her of the rights God has given you over her, and what He has obligated upon her in terms of obeying you in what is good. Your right over her is greater than the right of her family, and she is not permitted to allow someone you dislike into your house, based on the statement of Ibn Taymiyyah: "When a woman marries, her husband has more authority over her than her parents, and obeying her husband is more obligatory upon her." And based on the statement of the Prophet, peace be upon him: "And your right over them is that they do not allow anyone you dislike onto your bedding." We also wish to point out that it is permissible for children or their relatives to sleep in one room if each of them has a separate bed.