Earlier quoted context omitted.
I spent almost 10 years trying to avoid calling my mother and father in law by their first names. In my home country's language there are words for "mother in law" and "father in law" you can use in a second person context, but English doesn't have any. My wife has the opposite problem. She's gotten stuck calling my parents "Mr. XYZ" and "Mrs. XYZ."
My inlaws are addressed "mom" and "dad" - is that weird?
And if they don't like what you picked, you'll know pretty quick.