Rping isn't hard, just post what you think the character would do and say. YOu can read some threads in some of the rp sections for examples. You can put a characters thoughts and actions into one paragraph, but dialog is usually it's own paragraph or sentence, like in most books.
Looks like most of the characters are taken, good signs for this rp. I can try Littlefoot, unless someone else wants to do him. Or I can do 1 or more of my LBT oc characters. I've not done them in a while. Mim, a rainbowface (though in the strick lbt rps of the past she's adventured with the gang since she avoids the arguments the adults do, though she's around young adult, 18-19ish in human terms. Diver, one of Ducky's twin sisters, and a few others I've not rped in a while.
If more adults are needed I can try one of the gang's mothers. For mama swimmer I'd have to watch some of the 8th movie to see if I can get a feel of her personality, or if I did Petrie's mother I'd either do the 11th movie and or the tv episode where she's in a lot, forgot the name of it.