Dear Concerned,
Out of the above notes it is not clear where is your BIL (brother in law's) wife right now.
a. DO NOT FILE anticipatory bail (AB) unless FIR is registered - you will be suggested to file AB but it will be of no use - due to technical aspects hence file only after FIR is filed - INFACT as there is no automatic arrest in 498A and the cops follow the procedure - you need not to worry on the AB at all. Cops will call your BIL and persons named in complaint even before filing an FIR for generic enquiry and would refer for mediation if needed.
b. As the marriage has been done just a month and so back - you can not file Divorce - However give the audio recordings and also given the disability of your BIL you may look for option available in Annulment of marriage under section 12 of crpc.
c. It seems this family just got into this marriage to blackmail your BIL and his family and now wants to ectract money on false pretexts.
You may feel free to contact us through skype or call for free consulting on subject.
Best of Luck