We both call each other’s parents by first names. I’m half white/half Japanese (both parents born in Canada) and he’s white (English/Scottish/Irish).
We’ve started sort of calling them by their grandparent names- Grandma and Grandpa, Grummi, and Molly and Angus. All picked by them.
I call my mother in law “mother.” My wife calls my parents “father” and “mother.” (Not in English).
I also come from a culture (Indian) in which it is unacceptable to address an elder by given name. Any elder, even one who’s not related to you.
I call my in-laws by their first names; I’d have liked to call my MIL “Mom” since she’s been way more of a mother to me than my mother ever was. But I think it would make her uncomfortable, and I love her too much to do that to her. However, she does know how I feel, and I know she loves me just as much as she does the children she gave birth to. In fact, she’s told me that of all the daughters-in-law she’s had, and the one son-in-law she has, I’m her favorite kid-in-law. 
When my parents were alive, my husband called them by their first names.
We were both born and raised in Maryland, and are of northern European descent.
White Southern–I call(ed) my in-laws by their first names most of the time, although…I really can’t remember addressing Ed by name. 
Maybe I didn’t ever use it to his face. I do call my MIL “Ma” occasionally, when we’re all being really casual, because I’ve never called my own mother “Ma” so it didn’t feel too weird.
He calls mine by their first names when names are required, but sometimes he’ll call my mom “Ma” just like I do his. Huh. Hadn’t really thought about it before.
DH and I both–from day one of our marriage–have referred to the in-laws as “Mom & Dad.” Just seemed natural to us to do so, although we were both offered the use of their first names, if desired. Everyone was very pleased that we opted for the more familial address, and it was what we wanted as well.
I’ll have in-laws soon (and I’ve known them well for 4 years now) and I avoid calling them anything!
I realized I got this from my mom. It does NOT seem right to call them by their names, call them by ‘mom and dad’ or anything. I feel weird. Turns out that my mom feels the same way and she’s never actually called my grandma (dad’s mom) by any name ever. We’ll both just start what we’re saying, or tap on the shoulder, or maybe say “hey” as a starter.
Just like how it really freaked me out when my grandma told my boyfriend to call her Grandma… AND HE DID. HE CAN’T DO THAT.
Yeah, I have a weird hang up.
When I was growing up, my parents called their in-laws “mom” and “dad”. Consequently, I called my in-laws “mom” and “dad”, much to their surprise and pleasure, as the other children-in-law did not do this.
However, there is quite an age difference between my husband and me - he’s nearly 12 years my senior. For him to call my parents “mom” and “dad” would be very weird, as my mother is only 8 years older than him. So, he refers to them by their names - actually, he calls my mom by her common nickname rather than her first name.
My daughter-in-law calls us by our first names, and I’m absolutely fine with that.
Typo Knig called my parents Mister and Mrs Zappa.
My sisters-in-law were granted permission (by my mother) to call my mother by her first name but Typo, being a less-welcome addition to the family, was not so “honored”.
I call Typo’s parents Mom and Dad.
I call my mother-in-law Mom or Eunice (which she hates because her name is Virginia.)
Seriously, I mostly call her Mom. I’ve become closer to her now that my mother has passed away, so occasionally, when we’re kidding around, I call her Mother.
Before he died, I called my FIL Tony – my own father is just so strong a personality, I could never bring myself to call anyone else Dad.
My wife calls my father Pop, as do all of his sons and daughters-in-law. The DILs called my mother Mom.
I love my husband’s parents and would call them “Mom” and “Dad” in a heartbeat, if they ever asked me to.
Since they haven’t, I call them by their given names. I’ve never called them “Mr …” or “Mrs …”
My husband calls my parents by their first names as well. My mom did ask me to ask him once to call her “Mom” and I passed the message along, but he declined. 
You gals have to stick together 
It’s worth noting that Mama Zappa’s sisters-in-law called her father “Mr. Zappa”. I was not the most welcome son-in-law ever, but Mr. & Mrs. Zappa were also traditionalists who liked formality. Right after Mama Zappa and I were married, I shook hands with my bride’s parents and said “I guess it’s ‘Mom and Dad’ now!” “We prefer Mr. and Mrs. Zappa.” “Oh.” :o
My parents are “just don’t call me late for supper” types, and “gaining a daughter not losing a son” types.
And for the record, both of Mama Zappa’s parents have passed on. We may not have been pals, but I do miss them.
Himself and I are not married, but we live quite near my parents and about an hour away from his. We’re supposed to call them by their names, according to all of our relative ages and such. We don’t because it makes us both uncomfortable, but yet calling them Mr. and Mrs. Zsofia and Mr. and Mrs. Himself would get us corrected, and so we engage in the age-old practice of avoiding names altogether. We’re both Southerners born and bred, and have problems with this kind of thing.
I don’t know what Himself and my dad call each other at their Mason meetings, where presumably they’re forced to talk more.
I do not believe, if we got married, that I would call anybody but my own mama “Mom”. Maybe if my parents were long-dead and I had kids of my own.
I took a cue from my MILs and call them whatever they sign their e-mails to me. So my MIL is addressed by her first name, and my SMIL is now called Mom. (I did, however, talk to her about this, and I asked my own mother if she would be offended if I called my SMIL “Mom.” My Mom said it was ok with her, but I wanted to make sure before I started using that title for someone else. Just a matter of respect and courtesy to my wonderful mother.)
I call my SFIL by his first name, and I still don’t know what to call my FIL. He would be fine with Dad, or first name, or whatever, but because my own father is dead, I have a hard time calling anyone else Dad. After five years, I’ve yet to call him anything; I love him dearly, but I don’t know how to approach the subject. He is like a father to me, so I should probably get over it by now and just call him Dad.
My father often called my mother’s parents Mom and Dad, yet my mother never called his parents by anything other than their first names. He loved her parents; she (and he) couldn’t stand his.
SMIL? SFIL? Second Mother-in-Law? A polyandrist in our midst!
Heh, not quite. Step-mother-in-law and Step-father-in-law. Yes, I got the lucky bonus of two entire sets of in-laws, who hate each other.
Well, I only have one sister in law, and I call her by her first name. I call her mom by her first name, as does my brother (her husband)…
In Japan, people usually call in-laws otoo-san (Father) and okaa-san (Mother).
For me, I don’t talk to my in-laws, so I don’t call them anything.
Seriously. We don’t share a common language, as they don’t speak English or Japanese and I don’t speak Chinese or Taiwanese. Well, my MIL speaks some Japanese so I’ll call her okaasan but then have to point at what I want.
I called my ex’ mother Miss Ginger and his dad Pops. I called his step-mother Aunt FirstName (she was also his aunt, long story) and the step-dads Mr. FirstName. He called my dad Mr. Fred and my mother (among other names) Miss Ginger.
My step-son’s ex-wife called me Mimi and his dad Papaw (as do the g-kids) and my step-daughter’s partner calls us Mom and Dad.
My parents always called their inlaws Mom and Dad. Various SILs (former and ex) have always called my parents Mom and Dad as well. The BILs tend to call them Fred and Ginger.
My in-laws live with us so that may make a difference, but they don’t speak English, only Chinese. I just call them Mama and Baba, which is Chinese for (shocker) Mom and Dad. My brother-in-law (my wife’s sisters’s husband) calls them by their first names. They like me better than him, though. 
My wife calls my parents Mom and Dad too.
The greatest thing about my inlaws is that they live on the other side of the planet.
My wife calls my parents “Mom and Dad”.
I call her parents “어머 와 아버”.