Thanksgiving week is one of the busier stretches for a small fleet, and the bookings look different from summer. Summer is beach gear. November is people and suitcases arriving on the same flight.
Count the bags, not just the seats
The mistake is booking for the number of people and forgetting what they're carrying. Five adults fit in most cars. Five adults with a checked bag each do not.
The Range Rover seats five and has the cargo room to go with it, which is why it's the usual holiday pick. If the group splits across two cars anyway, the Fiat 500X is cheaper and easier to park at a house downtown or in West Ashley.
Book before the flights get cheap
The fleet is small. When a car is booked it's gone, and the holiday weeks fill earlier than the rest of the year. The booking page shows open dates live, so a date that displays is a date you can still take.
Pickup
Everything goes out from 1471 Folly Road on James Island. If your family is spread between Mount Pleasant and downtown, the lot is roughly in the middle of that, and the service areas page lists the drive from wherever you're staying.
Renters need to be 21 or older, and the person who books is the one who drives.