Hey there, Jennifer!
Welcome to the Disney Parks Moms Panel. I first want to extend a thank you to your father-in-law for his military service! The Disneyland Resort is very committed to showing their thanks to the military by offering
special discounts on theme park tickets, Disney PhotoPass packages, and Disneyland Resort Hotel stays.
I'm sorry that your father-in-law isn't able to join you on your vacation to activate these military park tickets. Unfortunately an active or retired member of the military or a military spouse with valid ID must be present at the gate upon arrival to activate these 3-Day and 4-Day Park Hopper tickets. If the military service member will not be present, the family members at the Disneyland Resort can take these military tickets to a Main Entrance ticket booth and use them towards the purchase of regular tickets, paying just the difference in price. Thankfully this means your tickets are still able to be used. The Disneyland Resort ticket booths open approximately one hour prior to park opening and close approximately one hour after the parks close.
Since you have a connection to the military, you won't want to miss the daily Flag Retreat Ceremony that happens each afternoon in Town Square of Disneyland Park. This patriotic tradition has been a part of the park since its earliest days. You can check the daily park schedule when you arrive to make sure you don't miss this iconic ceremony featuring the Disneyland Band and representation from each branch of the armed forces.
I hope this helps, and please return if you have any other questions. I hope your trip is Fantasmic!
-Jennifer