My husband and I just got married less than a week ago and neither him, his parents, nor I, know how I should start addressing them. I met his parents when I was 16 years old, so I was calling his parents Mr. and Mrs., which has continued up until now- 8 years later. When we got engaged, I stopped referring to them as Mr. and Mrs. and started awkwardly just saying "hey, how are you doing?" and "goodnight, thank you for _____" as my greetings instead (I don't think they noticed haha). Anyway, so now we're all feeling a bit weird about this change, even though both his parents call their in laws by their first names.
On the other hand, my mom and dad have requested that my husband address them by "mom and dad" in my native language because we're all family now. It'll take some getting used to, but at least we know that it's what my parents want from him in order to feel like a family but also feel respected.
Anyway, just curious how and your spouse each address your in laws!