My in laws never addressed the name issue either - I went almost 30 years of marriage (before they both passed) not really calling them anything - just talking to them! I may have called my FIL his first name a couple of times when I really needed to get his attention. It always bugged me not to know what to call them. I talked to my H about it and he always just shrugged his shoulders. He did call my mom “mom” - I think he just felt comfortable to do that.