Does your partner remind you to buy a card/present/arrange a day out on Father’s Day for your own father? Or does he just do it himself and send a card to his father in law from both of you?
YANBU - I’m a busy woman, I cannot fit in any time to send a card once a year without any prompt, especially as I’ll probably not even bother to do the same for my husband who is also a father.
YABU - He’s your father for goodness sake, you’re a grown woman who has a responsible job and can manage to plan around deadlines, and are you not planning to do something with your own children for your husband on that day too?