It is a little weird I guess, but counting the total years I have been with my husband (7 dating+married) I have never referred to his parents by their name.
When talking to my husband I just say "your mom" or "your dad."
And in person (with the in-laws actually being around) I do not call them anything! I guess I purposely avoid calling them by their first name or Ms. ________ and Mr. ___________ (his parents are not together.)
My husband also shares the same name as his dad so it would be soooo weird calling him by his name! haha.
We don't have any LO's yet but do have one on the way and I expect that when I am telling my LO to go to an in-law I will just refer to them as whatever LO calls them.

Do you call your MIL or FIL by their first name, when speaking to them or do you avoid calling them anything at all and just speak, like me?
any other in-laws you dont call by their first name?