Parents-in-Law. What do/did you call them?

My late in-laws weirdly popped into my mind the other day while I was chopping veggies. It occurred to me that I never, in the 10 years I knew them, called them anything. Gladys & Donal didn’t feel right nor slipped off the tongue. Mum/Dad wasn’t appropriate as I already had a Mum & Dad. Mother/Father too formal & uncomfortable. I must have mumbled something when necessary - heaven knows what! They lived for each other & died 40 years ago within 6 weeks of each other. Perhaps, subconsciously, I was remembering the anniversary. Strange to think I am the only one left who does and although we were never close, I feel quite emotional about it. Perhaps with the benefit of hindsight & experience, I would treat them differently than I did as a newly married 20 something.