Question on negotiating with debt collectors

Hello, r/personalfinance. If this is more of a legal question, please let me know.

My father-in-law recently received a call from a debt collector attempting to collect my wife's contact information. He refused to hand that info over and let my wife know. We checked out her credit report and saw that she has an account in collections from before we were married (about 5.5 years ago and the statute of limitations has not yet passed). She doesn't have any exact recollection of the alleged event causing the debt nor records of the debt itself.

We have not requested proof of validity from the CA yet (as she has not been contacted herself yet), but assuming they can prove that the debt is legit, we're willing to pay them. After doing some digging around on this sub and other areas of the internet, I believe that the CA may have violated one or more parts of the Fair Debt Collection Practices Act when they informed my father-in-law (in the aforementioned phone call) of the exact amount of as well as the nature of the debt (medical).

We've since moved from that state to another and I am curious if I can use the CA's communication with my father-in-law as leverage to negotiate, if I shouldn't bother including that in negotiations, or if I should wander over to r/legaladvice instead.

Thanks.