want a solution

Marriage of both is invalid. So get the mutual divorce concealing the subsequent marriages.

Instad of concealing the subsequent marriages , reveal the fact of remarriage of both and seek divorce,which may throw open a new ground for consent /compusory divorce

pray under the specific relief act or pray for mutual divorce to regularise the matter, instead of hiding the fact keep it before the court. because both the second marriages are invalid and void in the eyes of law.  which means there was no marriage. the only lawfull marriage is the  first one, but it is non existed right now. moreover the so called husband of the wife, can be sued by your brother under 497 of ipc.

after divorce your brother could be able to register his marriage.

in the registration form, your brother has to decleare that he has no living spouse. without divorce it will be a false statement, and liable to be punishment.

YES,BOTH THE  SECOND MARRIAGES ARE INVALID and to give it legal sanction ,you and ur 1st wife will ve 2 go thru mutual divorce to disolve ur 1st marriage....