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.
Your brother should advise his wife in a good and soft manner and clarify to her that intoxicants are forbidden and that they may cause many disadvantages and harms in her religion and her worldly life.
For more benefit on the evidence that intoxicants are forbidden, please refer to Fatwa 81900.
If his wife wants to quit consuming alcohol and treat her addiction, then she may follow the advice and guidelines that we mentioned in Fatwa 88545.
However, if she persist on consuming alcohol, then it is better for him to divorce her and look for a pious wife.
Finally, it should be mentioned that a Muslim should not hasten in getting married. He should rather seek advice about the woman whom he wants to marry and perform the Istikhaarah prayer before going ahead with the marriage.
For more benefit on how to perform the Istikhaarah prayer, please refer to Fatwa 81434.
Allaah Knows best.