Hello Heather!
Welcome to the Disney Parks Moms Panel! I hope you're having a magical time planning your next Walt Disney World Resort vacation.
Depending on what type of reservation you have, it may or may not be possible to add your son-in-law for only the days he will be joining you. If you have a
Magic Your Way vacation package then unfortunately, everyone on your reservation will need to have the same package details such as theme park tickets. If you have a room-only reservation and separate tickets, and have not exceeded the maximum occupancy for your room, then you should be able to add him.
I recommend
calling Disney Reservations to see what options you have to ensure you all have a magical stay. They'll be able to pull up your existing plans and offer custom suggestions specific to it.
Thank you again for visiting, Heather, and please come see us again with any questions you may have.
Magical Wishes,
Lauren