My question is that is it lawful for me to file false case against them to save me and my family from another false case.
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