The Koopalings all have alternate counterparts.
Larry Koopa - Abel Koopa
Abel looks a lot like Larry The only differences is Abel is older (THEY ARE NOT TWINS), his hair is a combination of pink and blue, he has horns, he has 4 teeth, he wears jeans, he has eybrows, his shell is pink with blue rings, and he has black wristbands.
Morton Koopa Jr. - Niko Koopa Jr.
Niko is a lot older than Morton. They don't even look alike (except they both are fat).
Wendy O. Koopa - Aiva O. Koopa
Like Morton and Niko, they don't look alike. Aiva is older than Wendy.
After a while, people started to make fanon koopalings
Alex Ember Koopa - Wyatt Koopa
They do look alike. They both are twins (Wyatt being older). Wyatt has more hair than Alex. Wyatt wears a headband because he is athletic.
Bazyli Koopa - Duncan Koopa
The both lost a part of their bodies. Nothing is really known of them.