I was married, and, I called my ex's parents a few different things...depended on the mood and the situation. I did sometimes call them "mom and pop," sometimes called them by their first names, sometimes called them what the grandkids did..."meemaw and pappy." honestly, i would either ask them what they want you to call them, letting them know up front that you're not comfortable calling them "mom and dad," or asking your husband to ask them for you.