They are the leaders of their respective groups.
They are very competitive.
They are the most outspoken and can be extremely stubborn.
They are pretty arrogant, selfish, and conceited, but will come through for their siblings in the end.
They enjoy extracurricular activities: Alvin commonly likes football or basketball, Brittany is into cheerleading.
Commonly they are the cause of many adventures/mishaps.
They enjoy the spotlight/being the center of attention.
They're not very wise to make decisions.