I disagree with Mr. TGK Reddy, your brother has already been awarded a decree of divorce by a competent Court of Law and his "remarriage" is legally valid.
However, his "ex-wife" may move appropriate Court for setting aside the decree, that is purely her own decision / concern.
Why are you worried about the matrimonial / divorced life of your "brother" if your statement is taken to be gosepel truth ? Let him seek opinion / advise from his counsel who is well aware about facts and cirucumstances of the case and an able, competent and intelligent enough to guide.
Do not adventure to disturb "him" and seek obligation of experts (although available FREE OF COST) on this platform.
If your "brother" is keen to seek second opinion it is advisable for "him" to consult another local prudent lawyer for better appreciation of facts, guidance and proceeding.