Related to 498A

My aunt's son married to my neighbor's daughter. After marriage they dont have any problems between them for a period, but after that the husband have a extra marital relation. And for this the relation between husband and wife detoriated. The married couple has a son also. A couple of years or more the wife living in her father's house with her son. Now, the wife comes to our house and blaming us that we are aware of her husband's extra marital relations and bad character - if you will not sort out the problem then I(the wife) will go to the court and file a 498A case against the husband and your family. We dont know anything about the husband's those type of acts, and we did not force them for marriage - they talked and made well enquiry about the husband and his family before marriage. Now my point is - 1) If the wife file any 498A against the husband and if there is any name of anyone of my family member - what to do? 2) When the court find us in the case not guilty then can we file a defamation case against them to compensate for mental harrasment to two senior citizen with physically unfit persons (my parents). - Please advice.