They do not make choices based on what they want to have, but rather on what they want to deny their brother.
They insist on watching something nor because they want to watch a particular show, they just don't want their brother to watch what he wants.
They scream bloody murder because their brother took a specific toy. Not because they really want to play with the toy, they just don't want their brother to play with it.
When told it is their turn to choose the shared snack, they don't choose what they like to eat, they choose what their brother dislikes.
it's not about making your own happiness. Its about making others unhappy. I'm hoping they outgrow it, because that is no way to live.