Finding the right tone for your father-in-law can be tough. You want to be warm but not overly familiar, respectful but not stiff. Here are exact words you can use.
"Happy Father’s Day! Thank you for always making me feel so welcome in the family. Hope you have a wonderful and relaxing day."
"Happy Father’s Day! Thank you for raising such an amazing person and for always making me feel so welcome in your family. Hope you have a wonderful day."
"Happy Father’s Day! Wishing you a great day relaxing and celebrating. See you soon!"
"Happy Father’s Day! The kids are so lucky to have you as a grandpa, and I’m lucky to have you as a father-in-law. Have a great day!"
"Happy Father’s Day! Hope you get to spend the day [golfing / watching the game / relaxing]. We need to catch up soon!"
"Happy Father’s Day! We are so grateful for all your support and advice. We love you and hope you have a fantastic day."
It’s a very nice gesture to send him your own brief text, even if your spouse is calling him. It shows independence in your relationship with him and makes him feel appreciated.
Use whatever you call him in real life. If you use his first name, use that. If you call him "Dad," use that. If you avoid calling him anything because you aren’t sure, just start directly with "Happy Father’s Day!"
Absolutely. It is one of the most common, respectful, and appreciated compliments a parent-in-law can receive.