Wife and Husband's Brother
Question

I have a very important question to ask you and this will Insha’Allah benefit many other Muslims. A friend of mine was telling me that a wife cannot come in front of the husband’s brother as he is not her Mahram. My question is this: I live with my parents and brother and sister. I and my brother pay the rent of the apartment.
Insha’Allah we are going to move to a rented house which will be bigger and the rent will be payed by me and my brother. I had thought of getting married because of the bigger house, but I don’t know whether I could do this now unless I get my own separate house.
Praise be to Allah.There is no harm in you and your wife living in one house with the rest of the family members you mentioned. All that you have to be careful about is that your wife does not go out in front of your brother or be alone with him in the house, because the Prophet (peace and blessings of Allah be upon him) forbade non-mahrams (unrelated men) to enter upon women. He said: “Beware of entering upon women.” One of the Sahaabah said to him, “O Messenger of Allah, what about the brother-in-law?” He said: “The brother-in-law is death!” (Reported by al-Bukhaari, Fath al-Baari, 9/330).
Al-Nawawi, may Allah have mercy on him, said: “What is referred to in the hadeeth is all the husbands (male) relatives apart from his father and sons. People customarily take the matter of a man being alone with his brothers wife as being of little consequence; to indicate the seriousness of the matter, it was likened to death. Indeed, one should be more cautious about the brother-in-law than about a stranger. The phrase “the brother-in-law is death” may have a number of meanings:


That being alone with a brother-in-law may lead to disaster if a sin is committed, or may spell divorce for the woman if her husband cannot contain his jealousy;
Or: Beware of being alone with a non-mahram woman fear this as you fear death.


All this stems from Islams keenness to protect households, to avoid evil and to preserve marriages in the best possible way. You will find more details under question #217 .
May Allah bless our Prophet Muhammad.