“Get them involved in teamwork situations where you compliment them as a duo, and they work together asdfadsf ”

Get them involved in teamwork situations where you compliment them as a duo, and they work together on a house chore, or solving a puzzle, or choosing a recipe for dinner. Ask them to help each other with individual tasks like school work so one's win is a win for them both. You might want to try separating them for playtime or even school so they feel independent.