The ruling on being alone with one's brother's wife and appearing before him in clothing without sleeves

Question:
This is also a family problem, and its cause is the brother-in-law. The sender, Fawzi Muhammad al-Najjar, says: When I returned to my country after a period of work here—and he means in Saudi Arabia after working for thirteen months—and after I had settled for a while, my wife told me: Your brother is coming here, and I meet him in clothes without sleeves, according to her words. I told her that this clothing is forbidden, but I did not give the matter any attention. However, two days before I was to travel, the owner of the house where I live told me: Your brother is coming to your house at twelve at night, and he did not add a word to that. His conversation with me was in a public place, and I was busy with my father and some people. Because of the many tasks involved in preparing my travel documents, I did not think about this matter. When I returned here, I did not give it any attention. But after a while, my wife began sending me letters. From these letters, I learned that my aforementioned brother does not go to see my children. So I wrote to her that I had learned my brother comes to the house at twelve at night, and this time is not appropriate. He also continues in his letter saying: I sent him a message and showed it to the father. The father, as if something came to his mind or thoughts, asks for a solution to this problem. What is the ruling on this action?

Answer:
There is no doubt that her going out to your brother in clothing that has no sleeves, and her exposing her face and head to him, and the like of that, is all forbidden. It is all a wrong and a cause of fitnah (trial, discord or temptation), and a cause of committing a major sin. It is obligatory to rebuke her and warn her against this action. It is also obligatory to rebuke your brother, and that he should rebuke her and not allow her to meet him in this manner; because a Muslim rebukes what is wrong, and fears Allah and hopes in Him (Glorified and Exalted is He), and he does not accept in his family, or in his brother's family, what Allah (Mighty and Majestic) has forbidden. He has no right to be alone with her, neither at night nor during the day. He has no right to come to her in the middle of the night when she is alone in the house. This is a place of suspicion and a place of evil.
Therefore, it is obligatory to prevent him from that and inform him that it is obligatory for him to come to her at a time when there is no seclusion, but rather in the presence of people, such as her father or mother, or the like. He should never be alone with her, neither at night nor during the day; because the Prophet (peace and blessings be upon him) said: And because seclusion is a means to committing a major sin.
Therefore, it is obligatory for you, O questioner, to strive to prevent her from this bad meeting, whether with your brother or with anyone else. Rather, she should be covered and veiled in the presence of all non-mahram men; because your brother is in the status of a non-mahram, he is not a mahram. She must meet non-mahram men with covering and hijab. And your brother should fear Allah and be wary of meeting her in a bad state, or coming to her at an inappropriate time; because in this situation, he is accused of what Allah (Mighty and Majestic) has forbidden. And because leaving her in her state and not rebuking her is a form of cooperating in sin and transgression. If you can, O my brother, bring her to be with you, then that is what should be done, so that you are safe from this fitnah. And Allah is the One to be asked for help. Yes.