Wife may not ask husband to divorce co-wife
1-11-2016 | IslamWeb
Question:
Assalaamu alaykum. I have been married to my husband for almost 26 years and we have 3 children. My husband married another woman in secret, almost 4 years ago, and they have a child. My husband actually cannot afford to spend on more than one wife. I am paying for the house and other expenses, like the children's education, and so on. He also does not provide to the other wife as he cannot afford to do so. He can also not be fair in terms of the time that he spends with my children. Sometimes, the children would only see him about 10 minutes in a day. His second wife has been asking for a divorce because she says that she does not love him and due to his inability to provide for her and her child. My husband has been reluctant to do this. Can I ask my husband to divorce the second wife since he does not fulfill the conditions to practice polygamy, which are: 1. the ability to provide for his wives, and 2. the ability of being fair in time allocation to the families.
Answer:
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 has been prohibited in the authentic Sunnah from the Prophet for a wife to ask her husband to divorce her co-wife; we have already highlighted this in fataawa 86783 and 86514, so please refer to them.
Also, the fact that your husband does not spend on his second wife is not a sound reason for you to ask him to divorce her; this matter concerns his second wife; she may ask for her right on him to spend on her, she may take her matter to an Islamic court, or she may be patient with him.
Your husband should be advised in a gentle manner, and it should be explained to him that he must do what he has been commanded to do by the Sharee'ah: to spend on his wives, and to be just between them.
Tameem Ad-Daari 
narrated that the Prophet said, "The religion is advice." They said, "For whom?" He replied, "For Allaah, His Book, His Messenger, and for the leaders of the Muslims and their masses." [Muslim]
Allaah knows best.