I would ask them how they would like to be addressed, and act accordingly.

^^ Me too!

Hello co-signers!

Another vote for asking.

My parents-in-law unfortunately couldn’t conceive…

I called them by their first names after we married and they asked me too. After the kids came along I found myself calling them Gramma and Papa. I still would if they were still here.

I totally avoided calling them anything at all when I could. If I HAD to address them, it was by their first names. The whole thing made me uncomfortable.
P.S. Love the name change. Hardly noticeable @samantha.

Traditionally, both spouses called their respective parents-in-law by the same name; for instance, husband called his wife’s parents “Mom” and “Dad” just as the wife did, or else, more formally, “Mom Smith” or “Mother Smith,” etc. Respectful family names, but probably not silly childhood nicknames.

My in-laws-to-be asked me what I wanted to call them, and I said I would like to call them what my husband called them. So they were Mom and Dad to me, while their other son’s wife called them “Bill” and “Mary.”

I don’t know when the first-names custom came along, but I didn’t and don’t like it at all.

Somewhat relevantly, when one of my sons was dating a former college classmate of his, she called me “Mrs. (Lastname).” The other was dating a young woman who worked in a billing office. She never asked, but simply called me “Jeruba.” One was following the custom and courtesy of an academic and familial hierarchy, and the other practiced the egalitarianism of the office workplace, where even a 100-year-old bookkeeper would still be called Gladys.

Mr and Mrs unless they specifically invite you to address them differently.
I have never addressed my in-laws as mom and dad to this day, 20-something years later.

For 40+ years I called my Mother-in-Law “MIL” and she called me “SIL”
It was a very personal inside joke between us.

I never would have wanted to call my in-laws “Mum” and “Dad.” I had my own parents. I called my MIL “Mrs—-” for years until we finally settled on her first name. My Ex called my folks by their first names and I invited my DILs to call me my first name pretty early on. That felt right to me but each to his own.

Same answer as @KNOWITALL.

My fiancé’s parents were Mr. and Mrs. So-and-So until we got married, then I switched to their first names.

I personally dislike calling in-laws “Mom” and “Dad”. Makes no sense to me. I already had parents.

Thank you all for the replies…

Agree with @cookieman – that’s how I felt.

Fortunately, early on, not long after I met them, they said “call me “Bob”, not Mr. <last name>.

How were they introduced to you? Did they ask you to call them by a certain name or title?

My first marriage I called them by their first names. My second marriage I called them Mom and Dad. It’s just Dad now and after Jeff passed away (and both my parents are gone), I truly feel like he is my dad.