Happily married with 2 children. My Wif'e parents died 5 years ago. Wife's sister, 30years old and not married, is very good to my children and treats them like her own. and she preferes living with us instead of living with her brother and his wife. She has no other family in the country we live in. She prefers being with us instead of getting married and moving away. For the past five years I have been taking care of her and treating her with the same kindness as i do for my wife. She depends on us for all her needs. I know that having two sisters in wedlock is not allowed, but can there be a special fatwa for our case? I want my wife's sister to have the same rights as that of my wife. My wife loves her sisters so much and would not mind if i marry her if it is allowed or if there is a fatwa for it.

All Perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as that of his family and all his companions.

Dear brother, you must know that combining between two sisters as wives is absolutely forbidden and it is a fundamental in Islamic legislation which is proved by Quran, Sunnah and the consensus of Muslim scholars. Allaah Says (that means):  {… and that you take [in marriage] two sisters simultaneously…}[Quran 4:23].

This prohibition is eternal till the Day of Judgment and covers all people; it is not peculiar to someone or certain cases. So, you are not allowed to marry the sister of your wife as long as your wife is in your wedlock.

We would like to say to you clearly that it is obligatory upon you to ask your sister-in-law to leave your house to live with her brother. You are not her Mahram (i.e. a spouse or a person whom one is permanently prohibited from marrying due to suckling, marital, or blood relations) and it is forbidden for you to be in seclusion with her or to shake hands with her. It is also forbidden for her to appear in front of you without observing complete Hijab. We fear that you will become attached to her passionately, if it has not already happened, and it may lead to evil consequences.

Therefore, you should fear Allaah and should not think of combining between two sisters as wives which is absolutely forbidden. She has to leave your house to live with her brother or any other Mahram, as this is safer and far away from any seduction.

Allaah Knows best.