Marriage legal or not?

Dear Lawyers, My brother married her gf two years back without the consent of her girl parents. She asked my brother that she want to keep the fact hidden until she convince her parent about marrying my brother. But it's been two years she has not revealed a bit and never turned up home. She is playing on with my brother and due to frustration my brother explained and narrated all the instances to her parents himself. To his surprise, they think that their marriage is illegal. Now, they married in a Gurduwara and had their marriage registered at the registrar office. Now as far as I am concerned, I know it's legal. But her Maternal Uncle who happens to be a lawyer thinks otherwise and also made a fool of my brother by saying that, you registered your marriage and it's not a court marriage so it's not legal. To me, it sound completely garbage. But I would like to knw how we can proceed to get the divorce as her parents has completely refused to give divorce and want her daughter to marry someone else. Please advise.