Your brother will not press charges for bigamy.
Your marriage is void ab-initio as there was a wife living and the first marriage was subsisting during the time of your marriage and hence your marriage has no legal binding. His first wife is the aggrieved person and she had the opportunity to press bigamy charges against your husband. You will only be considered as aggrieved person w.r.t section 375 and not for bigamy. But then section 375 doesn't apply to you as you are willingly entered into the wedlock.
I would suggest you to leave aside all these legal complications and get married to him again now to keep your marriage sane from all legal complications.
You file for void and null marriage immediately. Your brother has no legal stand except a right to file an FIR but that will fall flat and gets dismissed in your absence at the prosecution.