Action against a chartered accountant

Signature of the assessee is required for filing income tax return, without signature return can't be filed. CA's ussually get return signed from his client. In your case it may be happend that your inlaws are singing your wife's return because I don't think any CA sign his client's return.

No CA undertakes this risk to sign in original any others return by himself... it is highly likely that your in laws are the ones who has signed the returns..... now yu are more concern with your inlaws filing returns without your knoeldge so first talk to them letting them know about implications for the same.... once they are caught...