So, in this alternate universe...Uma will play as Ursula. She'll be in the cave doing sea witch magic. Mal will play as Ariel and go do whatever Ariel does or something.
Mal's siblings will play as Ariel's sisters. Unless you're a guy...Then you're still Mal's sibling.
Harry can be Uma's sidekick mermaid.
Celia can be The little fish that sticks with Ariel. Except she'll be a Mermaid not a fish..
Dizzy can be...Sebastian...
You already know Ben will be Prince Eric.
Everyone else who's an OC is a mermaid or merman!
There! Let's start.