1. Rupees One lakh or two Lakhs, taking dowry is a punishable crime,
2. It does not matter whether it was asked or not, the evidence that dowry in the from of cash was taken is enough to be prosecuted,
3. So, never ever admit that cash was accepted. If the cash was accepted through cheque, refund it by RTGS to the account no. from where it was credited,
4. If you have any evidence that she had informed you that she has already passed engineering, then you brother can file a petition for annulment of marriage for availing his consent of marriage by suppressing the vital fact and had it been informed to him, he would not have agreed for the said marriage,
5. If there is no such evidence, then wait for one year of completion of marriage after which either he can file a divorce suit or can negotiate with the girl and file a mutual consent divorce petition.