Based on the facts before us the second marriage in the lifetime of the first wife is void under S. 5/11 HMA
S. 5 HMA lays down as;
". - A marriage may be solemnised between any two Hindus, if the following conditions are fulfilled, namely:
(i) neither party has a spouse living at the time of the marriage.”
S. 11 HMA further provides as;
"Any marriage solemnised after the commencement of this Act shall be void and may, on a petition presented by either party thereto, be so declared by a decree of nullity if it contravenes any one of the conditions specified in Clauses XXX of Section 5."
This section clearly lays down that if the marriage is not performed in accordance with the provisions of S. 5 (i) HMA, which is your sisters case it would be null and void and either party to such marriage may also get a declaration by a decree of nullity from a court of law.
See, it, however, could not be the intention of the legislature that such a marriage would be valid till it was declared a nullity by the Court. For a marriage which was void ab initio no such declaration was at all necessary. If the intention of the legislature had been to the contrary, specific provisions must have been made in the Act. But the Section referred to above is perfectly silent on that point. So, it is clear that the marriage which had been performed in contravention of the condition mentioned in Clause (i) of S. 5 HMA would be null and void.
A marriage which contravenes the conditions referred to in S. 11 HMA is in law no marriage at all being void ipso jure and it is open to the parties even without recourse to the court to treat it as a nullity. Neither party is under any obligation to seek a declaration of nullity under this section though such a declaration may be asked for the purpose of precaution or record.
There is a huge difference in a particular word that you use in your facts "annulment" to rest of the facts and what whosoever guided and is guiding you above which I can clearly read I differ in totality to all of them and let me explain to you now how to go about it once above provision of Law is clear to the family supporting with my below detailed reasoning;
A marriage which is void ab initio does not alter or affect the status of the parties nor does it create between them any rights and obligations which must normally arise from a valid marriage except such rights as are expressly recognised by the Act. There is a distinction between Section 11 and Section 12 which speaks of voidable marriages as distinguished from void marriages. A voidable marriage remains valid and binding and continues to subsist for all purposes unless a decree is passed by the Court annulling the same on any of the grounds mentioned in Section 12. These distinctions in the effect of void and voidable marriages are well settled by various Hon'ble High Courts as well as by Hon'ble SC.
The distinction is further indicated by Section 17 which makes the parties to void marriage criminally liable, while there is no such penalty for the parties to a voidable marriage. Of course, both Section 11 and Section 12 speak of a decree of nullity; but Section 11 speaks of only declaration of the marriage as null and void by such a decree, while Section 12 speaks of the annulment of a voidable marriage by a decree.
As your sisters void marriage is non-existent in the eye of law, only a declaration of the marriage as null and void is sufficient.
Whereas in case of voidable marriage an annulment is necessary because such a marriage shall be deemed to be valid until it is annulled by a decree of nullity. The effect of a decree of nullity in case of a void marriage or annulment of a voidable marriage, is to render the marriage null and void from its inception for all intents and purposes.
So all at this stage your side is to do to provide some sort of court record to second man since he is asking is to go for "declaratory suit for declaration of the marriage as null and void " in a Civil Court. Use first man's last known address and get the marriage declared as null and void whether it takes 1 month or 1 year it will be always be in her favor. For the same her second man has to wait bze he is taking precaution and wants to see some sort of court record before re-marrying with your sister whereas laws clearly says not required but except for purpose of precaution and record.
Also you need not have to worry what first man is going to do once he comes to know about it, ask then to him why he was all these times trout fishing in The Himalayan waters!