The father of one's spouse.

पत के पिता

English Usage: I visited my father in law's house last weekend.

Hindi Usage: मैं पिछले सप्ताहांत अपने ससुर के घर गया था।

Plural form of father-in-law, referring to the fathers of one's spouse.

पति के पिता

English Usage: My fathers-in-law are both retired teachers.

Hindi Usage: मेरे पति के पिता दोनों रिटायर्ड टीचर हैं।