Hey Howdy Hey Christine and welcome to planDisney!
Such a crazy situation that Hollywood Studios filled up that fast! Looks like you have family coming in as well to experience the parks so let's talk about options on what to do from here and maybe some other entertaining options.
The first thing I would recommend if you are set on Hollywood Studios for the whole day is to keep checking for
Theme Park Reservations daily. Several times per day even. Other people may choose to change their plans and Disney might choose to change capacity for the day, so keep checking!
The other option that you have is to upgrade to a
Park Hopper with your tickets. It looks like as of now, EPCOT still has availability for the day. So follow me with this plan. Visit EPCOT in the morning for
EPCOT International Flower and Garden Festival, there is plenty to do eating your way around the world with all of the fantastic snacks and drinks and plenty of attractions to experience in the morning like the newly opened
Remy's Ratatouille Adventure. Then close to 2:00 p.m. hop on
Disney's Skyliner system over to Hollywood Studios and plan on shutting down the park at the current 9:00 p.m.
close time. Sure it is not a full day, but you will still get to experience the park for a good 7 hours. If you can purchase
Genie+, you can make Lightning Reservations for Hollywood Studios while you are in EPCOT and traveling over, so this may also help make efficient use of your time in the parks.
There are so many things to do and experience in each of the Disney theme parks that you are sure to have a great time. Plus an opportunity to ride the skyline adds to the unique experience! Good luck with your continued planning and keep checking those reservation sites!
Have a Magical Day,
Nick