I’ve been married for about 10 years and I still hesitate when I have to address my parents-in-law. They strongly prefer Mom & Dad more than their first names, and within reason, I like to call people what they like to be called.
I never did call them that, despite their wishes. It just couldn’t come out of my mouth. Luckily, we had kids, so I reverted to Grandpa and Grandmother (her preference).
I think insisting that an adult now call you Mom or Dad is silly. You are not the adult’s parents. Obviously, some people’s MMV.
I am extremely thankful that my in-laws are happy for me to call them by name. I would have had great difficulty in referring to them as Mum & Dad.
I am not married, but I’m with you. My Mom is Mom. I would not be comfortable calling someone else that. Dad has passed and for that reason it might have even more difficulty - as if I were not honoring his memory.
I agree that calling someone “Mom” who isn’t your mother is both awkward and odd. My husband calls my parents by their first names or nicknames.
If you have children, it becomes much easier. Then you just call them “Grandma” or “Grandpa.”
I’ve been married for over ten years, but have only ever called my parents-in-law by their first names. I am another that just can’t do it. I can (and sometimes do) in writing, so a card or an email from me might be addressed to my MIL as “Hi, Mom!” but never aloud.
My husband calls my parents by their names too. He has called my Mom “mom” once or twice but it never took. My father though, he always called by name and never attempted to call him “Dad”. He does say things like “Mom called today…” referring to my Mom or his, so I never know which one he is talking about. 
Until a year or two after my wife and I got married, I managed to avoid referring to my in-laws by any name whatsoever. Now I just call them by their first names, or Poppy/Nahnah/Grandmother/Grampaw.
I can’t bring myself to call my wife’s parents by their first names, even though they’ve asked me to: it was far too deeply ingrained into me early on that one simply doesn’t address a family member, family friend or even an adult stranger who’s a generation older than you by name. Heck, I didn’t even KNOW the names of my uncles, aunts, even grandparents for quite a long time, I had to figure it out by context when my parents talked about them! The Chinese language has different “titles” to distinguish among them by father’s/mother’s side relationship, whether a given aunt/uncle is older/younger than the father/mother who’s the blood relative, and in the case of ties, numerical indexing. But they’re not Chinese, so now what?
Now that I have kids I can refer to them as “Grandpa” and “Grandma” in the third person (my own parents designated with their Chinese titles), but also find it awkward to address them as such in direct conversation. “Mr. Lastname” or “Mrs. Lastname” seems way too formal, but as I said, using a first name is out of the question for me. So mostly, I’m afraid, I grunt or make eye contact and just start talking, or wait for them to talk to me first. Which could in the end seem the rudest option of all, but, well, there you have it.
Stupid, isn’t it?
Same here. Been married almost 10 years and still call them Mr. and Mrs. So and So. I could never see myself calling them Mom and Dad.
My grandmother and mother never really have cared for one another and to this day when my grandmother sends a card to my parents she signs on one line “Mother” and on the line below it “Mrs. So and So.”
She NEVER would have asked my mother to call her Mom.
Love my in-laws very much, but no “mom and dad” from me. Its definitely first names.
When I first met my gf’s parents, we actually discussed this topic. I jokingly said that he looked like a “dude” and she looked like a “sugar”. I was kidding. But they got a kick out of it and mentioned it to a few other family members. Somehow it stuck.
So feel free to give “dude” and “sugar” a try.
I call my mother-in-law “mom” because she’s in a nursing home, bedridden and doesn’t seem to get many pleasures out of life, so this is one tiny way that I can make her a bit happier.
I’m glad I am not the only one. Mom and Dad just seem odd, even though my own Mom and Dad weren’t good parents.
But I also have trouble calling them by their first name.
sometimes I’ll call them Grandma or Grandpa even though I don’t have kids since the brother had kids. Mostly I just don’t call them. 
I’ve been married over a decade and call my inlaws “Mr. and Mrs. (Lastname).”
I just can’t call them “Mom and Dad” - I have a mom, and my dad died several years before I married, and I don’t like transferring that title onto someone else. (Especially because my father-in-law really did not like my dad, and FIL is not a good excuse for a human being.) Plus they’re much older than my parents, so it wouldn’t really feel right to call them their first names, either.
Once, early in my marriage my FIL was doing what I interpreted later as possibly a passive-aggressive remark at me, talking with a couple of people about how one of the sons-in-law called him “Mr. (Lastname)” and how that was just weird. It wasn’t until much later that I thought about it - all of them do that.
Nope. Mom and Dad are my parents, not his. But happily, they don’t expect me to - I call them by their first names.
I’m glad I’m not the only one like this. I propose we start calling them Mil and Fil. 
My EX-in-laws still want me to call them mom and dad. I couldn’t even consistently call them mom and dad in the 5 years of marriage. I tried for the first few months but was never comfortable with it. This made it very awkward for me since ‘uncle’ and ‘auntie’ also didn’t seem appropriate. What makes it even harder is that my ex-wife still calls my parents mom and dad. Bitch.
I hated the idea of calling my inlaws Mom and Dad, but my wife was the last of her siblings to get married, and the other spouses toed the line and called them Mom & Dad, so the precedent had been set. Also, my in-laws specifically asked me to call them that, and made it clear that calling them by their first names would not have been appreciated.
On the other hand, my parents asked my wife to call them by their first names. I hate the lack of familiarity I have to use with my in-laws, not to mention the fact that I already have a Mom and Dad. Also, my in-laws frequently drive me absolutely bat-shit crazy, because I think they are both certifiable bat-shit crazy.
It feels weird to have it come out of my mouth, but I do call them mom and dad. It took a good 9 or 10 years to do it though. I loved them when I first met them, but they were difficult during the wedding phase and soon after our marriage when we moved out of state. Things gradually improved, especially after our son was born. Finally, I tested it out and the earth didn’t suck me in.
Now, over the years they have been extremely generous to us - kitchen renovation, a number of cars, large 40th birthday gifts, trips. And they really adore their son and our son. And I realize that I played a role in any discomfort between us. So, I feel like it’s the least I can do so I do it.
I have quite possibly the world’s greatest in-laws, and they still don’t get Mom and Dad from me, even though they’re more present in my life than my own parents are. It’s just weird.