My MIL and I are civil and appropriately affectionate, but not that close. I call her by her first name, though she has dropped many hints over the years that she’d like me to call her Mom. That ain’t happenin’, though, only my mom gets to be called Mom.
What about you?
I call her mom. I asked the others what they call her and that’s what they told me. My family is rather annoyed by it, as they too feel that should be reserved for my mom. Except my mom called her MIL mom, so I don’t get it.
I got the sneaky out because my MIL is Japanese. So I am able to call her “Okaasan” (mother) without it having the emotional impact of “Mum” which I would use over my dead body.
The better I have got at Japanese the less I have liked using “Okaasan” and as soon as the kids were born I switched to “Baachan” (Granny). I got a few grumbles about “I’m not YOUR grandmother” but I ignored them because I’m not her daughter either.
(And no, I don’t like her!)
Mrs. (Lastname). Two of my husband’s sisters are married and both of their husbands address the inlaws that way as well. I know that at least my father-in-law doesn’t prefer that, and I’m not sure which (Firstname vs. “Dad”) he’d prefer, but we just don’t do it. I wouldn’t switch to “Dad” or “Mom” if asked; I pretty much loathe my FIL for good reasons and am not always the happiest with my MIL though she’s a walk in the park compared to her husband.
Same here*. I use the English “Mom” for my own mother and the Japanese for my MIL.
*Although she and I get along great. Could be related to me marrying a daughter, while you married a son? Or just that some people are nice while some are jerks.
Bitch.
Really. I do. When we’re civil, I call her by her first name.
I call my in-laws Mom & Dad. My husband calls my parents Mom & Dad, too.
My mother always called my dad’s parents Mom & Dad, so maybe that has something to do with it. Although my father called her parents by their first names.
When talking to my wife about them they’re “Your Mum/Your Dad”. When talking to them, I use their first names.
We’re all very polite and friendly to each other, basically.
“Your mother”
I use her first name. She asked me to when we first spoke in the phone (she lives quite far away and I didn’t actually get to meet her until my wife and I had been married two years), and I’ve done that ever since.
Mom. Or Miss Jean.
Everyone on hubby’s side of the family calls her Mom. Even her grandchildren! I always thought that was a bit odd, but oh well.
My mom has passed away, so there’s no conflict about that. My kids’ Grandma, I called her by her first name. She recently passed also. 
I was introduced to the in-laws, probably nine months (heh) before they became same, as [firstname] and [firstname]. I’ve never been told I should call them anything else. Wife’s sister’s boy (not son but boy) calls them by their firstnames.
Wife calls my parents by their firstnames. So does my sister’s husband.
This might be because my parents’ parents were addressed differently by their children-in-law and my parents want to be different (and Og knows they have their reasons, at least in my mother’s case).
My wife and I call each others’ parents by their first names, usually. But her father is named Paul also, so he’s sometimes referred to by his full name.
Indeed, when you have a name like Paul, you get used to that. Every Tom, Dick and Harry is called Paul.
First name or Grandma - if the kids are around.
I call both mine (I have a MIL and step-MIL) by the first name. They’re both lovely (though very different women), but I couldn’t imagine calling anyone but my own mother “Mum”.
I did, on my wedding day, ask in a jokey sort of way if I could call my FIL “Dad”. I’ve never met my own father, so the name doesn’t have any emotional connection to anyone, and it’d be nice to have a father-figure reaction. But I couldn’t gauge by his reaction whether he liked the idea or not, so I didn’t push it and just stick with his first name.
My SIL and I are very close, and she gets on so well with my mum that she’s asked to call her “auntie”!
I love my husband’s family, they’re wonderful people. Reading some of the other responses in this thread has made me very grateful for that.
Mom (and Dad), and I hate it. My biological parents are my Mom and Dad, not these two that I unintentionally inherited when I fell in love with and married my wife.
My parents asked my wife to call them by their first names; I tried to adopt that same system with my in-laws but they actually told me to call them Mom and Dad. Their justification was that they already had a son- and daughter-in-law that did it that way, so it would be easier. I don’t see how that makes it any easier for me, since it grates on me every time I’m forced to subscribe to it, but I keep my mouth shut. There are enough other things I disagree with about their actions and comments that I pick my battles.
I call her Mrs. (Lastname). For the first couple of years she asked me to call her by her first name, but I told her that I couldn’t do it. I was raised to call the people in the generation before me “Mr.” and “Mrs.” (I don’t remember what I was supposed to call single women - strangely, I don’t think that ever came up). Now that we have kids I mostly call her Nana.
At the beginning, I think she thought that I didn’t like her because I wouldn’t use her first name. After she met my family and every one of my brothers and sisters called her “Mrs. Lastname”, she understood that it is not a reflection on how I feel about her. In fact, I like her very much but I’ll never be able to call her Mom or anything other than Mrs. Lastname.
I still call my first MIL “mom”. She’s a sweetheart and I love her so it was never an issue for me.
We talk regularly although I divorced her son in 1985. I stop to visit her whenever I go through or near Virginia,
I call her by her first name. She’s a lovely women, but she’s not my mum.
It’s a long story - Japanese MIL-ness and attempting to bully the lowest on the ladder (me!) was attempted but I fought back. Some of it is because she is an ignorant peasant (sorry but she is, factually that - no education because it was interrupted by the war and brought up by an animistic mother who passed on a lot of her beliefs) and some of it is because she simply cannot hide how very, utterly, unimportant I am to her now I have produced the heir and a spare.