Hiya Penny!
Welcome to planDisney! What an amazing grandparent you are to take the kids to Walt Disney World Resort this summer! They will have a magical time and so will you.
If their dad is purchasing the passes online he will be asked to verify his residency online easily by entering their valid Florida driver's license, valid Florida state-issued ID card, or valid Florida-based military ID. Once that is done due to the nature of
Annual Passes that are newly purchased, they must be
activated in person as well. Every person who is 18 years of age or older must present their valid Florida ID at any Theme Park ticket booth or Guest Relations. This is so that the Annual Passholders can get the special card that will allow them the full benefits of being an Annual Passholder such as discounts on merchandise, free Theme Park Parking, and the ability to check-in to their
Annual Passholder discounted Resort room. I don't know the ages of the children but if they are Florida residents and their father verified the residency online they will be fine to enter the Parks. Just make sure then when activating everyone's cards the people who are getting activated are present and if they are 18 or older must provide evidence of valid Florida residency again.
I hope this helps, If you have any questions
let me know!-Nimmy