What to call your in-laws if not their first name?

 I think I maybe called my MIL and FIL “Mom” or “Dad” less than a handful of times in the decades that DH and I have been together. FIL passed away over 20 years ago, so he mostly hasn’t been in the picture, MIL and my mom passed eight years ago so now it’s not an issue at all.

Mostly I just avoided it entirely by speaking to them directly and not using any name, and I would do the same as mentioned above when referring to MIL by saying, “DH, your mom is on the phone” or whatever. It really is pretty amazing how long you can go without ever using a person’s name.

And LOL the grandparent name thing, I didn’t have my kid until the last year of my mom’s life (she would have been 84). But because of my much older siblings, she had a passel of grandkids before mine so she had been a grandma for decades prior to my kid coming along. Most of us would call her Granny all the time, as in, Granny Fanny Nesselrode who was a gray curly haired granny puppet from Sesame Street! She would say she hated it, but we all knew better and kept calling her that anyway. 

I think after 12 years that ship has sailed. If the person didn’t say something sooner, I’d come up with something really aggravating and start calling them that instead and see how fast they change their tune, but I can be amazingly passive aggressive like that when I want to be. And I’d be calling them Mr/Ms Asshat in private.

Speaking as the mom of a transgender child, I've had a lot of learning in the "what you call someone" area.

What I've come away with is they should be called as they desire to be called.

I've also learned it's not my job to figure out what to call others. It is their job to decide and to share it w/those they love.

So, I think it's your parents' job to come up w/how they would like to be called. Not yours.

PS - It's never "too late" for someone to change what they are called.

My dad and all the other son in laws called my maternal grandparents Mother and Father, so I got nuthin'. I don't know what my mom called my dad's mom. She lived in Croatia, and I was 5 the one time I met her, my dad's dad died before her came to Canada,

Everyone in my family called my uncle's (mom's brother in law) dad Opa.

My parents are Nana and Dida to the grandkids; my brother's in laws are Grandma and Grandpa.
In fact, my mom's other two sisters are also Nana. The one grandpa is grandpa, and the other, before he passed away, was Opa.

They need to decide,

I think you need to come back and fill us in on the cultural norm OP and if they are requesting Mr./Mrs. or Mom/Dad - I think it makes a difference on how you navigate. I can certainly attest that one can go a long, long time (I think my mom said 30+ years without using someone's name - her MIL). It does seem for my generation that grandparents picking different names for themselves for their grandkids than grandma so many people I know use that name themselves. My MIL and FIL are Nana and Papa and my cousin uses Gigi and Pop which is what her inlaws asked to be called by the grandkids. I also know lots of family members who use their inlaws native language for mother/father and it feels very different than calling them Mom/Dad - my cousin calls his MIL Ina for example.

What about mother/father in their native language - or is it english as well?

How about Mil and DIL (Mom in law and Dad in law) ? Since they suggested the MIL and not FIL 

How about MIL and DIL (motherinlaw and dadinlaw) since FIL sounds like Phil.
Or what is MIL and FIL in their first language since the issue if cultural. Maybe the first language cultural names or a variant on that would work.

It is strange that they don't want to be called by their names, but they need other people to help them come up with what to be called. After 12 years.

You said using mom and dad is off the table. Why?

I think in-laws should say, “Call me ____” and that it’s polite to call them that

I avoided calling mine anything at all for years. I was not comfortable calling them mom and dad and they were not thrilled with being called by their first names. I’ve now been married to their son for over twenty years and just use their first names, but I am reading the suggestions here with interest.

I'd wait until grandbaby is born and do a grandparent name; Nana, papa, whatever.

I'm amazed at how many people seem to be able to interact with their inlaws without calling them anything. What do you do if you need to get their attention?