Aslkm! this is my 2nd mail regd this subject. I didnt got reply to my first mail. same question again. I want to marry a girl who is my relative. My relation to her is - she is my cousin sisters daughter. Can i marry her according to Shariah. As her sister calls me brother(not own), is it permissible for me to marry her with the aspect of islam. Please let me know the answer, as my future decision depends on your answer.
Thanking you
Mohammed Ali

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.

It is permissible for you to marry the daughter of your cousin sister as she is not a Mahram to you. Indeed, after mentioning the women whom we are not allowed to marry, Allaah Says (what means): {…All others are lawful…}[Quran 4:24]

The fact that her sister calls you brother does not make you Islamically a brother to her.

However, she might be forbidden to you in some other cases, like if she is your suckling sister [meaning that you and her suckled from the same suckling mother], in which case she is permanently forbidden to you, or that you are already married to her sister or maternal aunt, in which case, she is temporarily forbidden, because it is forbidden to marry two sisters at the same time, and it is forbidden to marry a woman and her maternal or paternal aunt [at the same time]. For more benefit, please refer to Fatwa 85868.

Allaah Knows best.