it is o.k. for a brother to marry again but is it ok for him to want to marry a married sister if the feelings are mutual what is her position being married with no caused for a divorce
Wa Alaikumus Salaam,
A woman who is married cannot marry another person. Hence, in the above case, the brother cannot marry to the sister who is married. This is totally haram and unlawful. If the woman is divorced, or her husband dies, then after the passing of the iddah, the sister can marry this brother.
The mutual feelings you have hinted to is not allowed. The things which would have led to this were totally haram, and both must immediately put an end to any sort of communication or contact. If these do not stop, then it will ruin the marriage.
And Allah knows best
Mufti Waseem Khan