It's your birthday, but I have the best brother-in-law in the world! I hope you have a beautiful day and that you have a lot of fun!
It is a privilege to have you in my family and to be able to count on your friendship. I highly value your presence in my life and I hope I can continue to count on your companionship.
Congratulations, my dear brother-in-law! Come another twelve months full of joy and wonderful things.