بسم الله الرحمن الرحيم
It is lawful for you to take any step to defend the fake cases filed by your wife and in-laws but filing false case shall be haram as it involves lie and deception; hence you should avoid it as such person will be awarded Jannah according to hadith. Supplicate Allah and recite the following dua extensively, in-shaAllah, your parents shall be protected.
حَسْبُنَا اللّهُ وَنِعْمَ الْوَكِيلُ
Allah knows Best!
Darul Uloom Deoband