Hi April - welcome back to planDisney!
You've picked a great hotel -
Disney's Art of Animation Resort is located on the
Disney Skyliner which will make it super easy to get to
EPCOT and
Disney's Hollywood Studios.
The Little Mermaid rooms are the furthest from the Disney Skyliner entrance so I'd like to share a tip with you. You may notice that a line will form for the Disney Skyliner at a peak time in the morning when everyone is trying to get to the parks at the same time. The line will form on Disney's Pop Century side so it may be quicker for you to join the line by walking through Disney's Pop Century Resort from your room instead of walking through Disney's Art of Animation Resort. The line will move quickly and the morning rush is typically the only time I've seen a line form for the Disney Skyliner.
Regarding your question, when I have multiple rooms booked for my travel party, I call
Disney Resort Hotel Reservations and ask a cast member to include this information on our reservations. This is also a great time to add any other room requests you may have. They will do their best to assign your rooms as close as possible for your vacation. This has worked for me each time so hopefully, it will work for you as well.
By the way, have you thought about reserving a suite? Depending on how many people you have in your travel party, it may be an option to reserve a suite instead of two separate standard rooms. The cost wouldn't be that much more than a purchase of two standard rooms. A suite allows up to six guests and they are super convenient. Your parents would be able to stay in the bedroom with a queen bed and their own full bathroom while your family would be able to stay in the main living area which includes a Murphy bed and a pull-out sofa that will sleep four guests. There is a second full bathroom available along with a kitchenette. Your parents could then reserve a Little Mermaid room for the additional nights they would like to add on. This may or may not work for you but I wanted to let you know that is certainly an option.
Have a magical vacation!
Diane