U are acquitted in 498 a only, but what about the other aspects.Are DV and divorce cases in the offing? If so U have to be extra alert. Once acquitted in 498 a, don't take it for granted,UR wife can file it again. I don't suggest defamation,perjury etc right now.
Father in law means 'in law he is your father'. If it is so , you being a son in law cannot file a case against your father in law. It looks indecent. But if you say it is just to take revenge against him in that event also my advice is to refrain from doing so. If you keep silent your image in the society will be brighter. Besides, we the experts do not advice or opine on unethical or revengeful acts and in fact we do not indulge to do so..So my advice to you is give up this idea.
Law and judiciary system should arrive at the trust , punish the guilty and protect the innocents.
File Wirt Petion (Article 226 and Article 21, 19, 14 & 15) With Indian Evidence Act 1872 by annexing your copy of evidences and other grounds
against the STATE only for violating the basic constitutional rights of you and pray for cost & order / direction to register FIR against the culprits. You may get minimum 10 lakhs as cost. Please also do the same in-person.
Also file both criminal and civil defamation cases against her and in-laws.
Please read each of my posts carefully in the following links for sample petitions and other necessary clues.
It is an acquittal in 498A, may be because the prosecution could not prove beyond doubt, hence any counter case will not be meaningful. Moreover, how come your father in law has filed cases against you?, what about your wife, has she not come into picture?, you have stated that only Sec4 of DP act is pending?, what do you mean by that?, whether that case has been filed separately other than 498a? What is your lawyer's opinion?, in any case no case for defamation will be maintainable. Moreover your action may prompt her to either go for appeal or file a fresh case within her jurisdiction and also mshe may file DV case too. For the present wait and watch the developments silently.