Hello, Mikaylah!
Welcome to planDisney, and thanks for sharing your question with us. I have a solution for you, so let's get to it!
Since half of your family has already secured park reservations and your dates are fully booked for Guests holding regular tickets, the best option is to
book a room at a Disneyland Resort hotel.
This is a good plan because Disney maintains a separate park reservation inventory for Guests staying inside the Disneyland Resort. This rule applies to Disney's Grand Californian Hotel & Spa, the Disneyland Hotel, and Disney's Paradise Pier Hotel, and they're all great alternatives.
To check availability when reading this answer,
look at this calendar. If you see reservation availability for your dates, you must book a room for your family members and link the hotel reservation to their Disney accounts. This should enable them to access the park reservations, and they should be able to secure their desired parks as long as there's still availability.
It's essential to move fast if you choose this option, and I wish you luck in booking everything you need, Mikaylah!
May the magic be with you,
Julie