Sorry for the wait on this artyfan xx I haven't read the new book (I know that involves the Fowl twins) so this isn't based on it xx Please review!
Beckett was very different to the others in his family but his eldest brother in particular. Artemis was, and there was no other word quite for it, cold. He smiled - sometimes - but it was like he was trying rather than actually expressing emotion. It seemed forced. But it was better than before.
In the rare recordings of Artemis when he was a child he didn't smile at all, and stood stoic and silent. (He even seemed to hold back on his usual witty commentary.)
Beckett on the other hand smiled constantly. Myles regularly complained it was annoying him. He was also a complete chattabox. Beckett was unlikely to shut up for the Queen and even less likely to stand still for any extended period of time.
On the surface they were like chalk and cheese, black and white. (But beyond that they were the same.)
Artemis was trying. He'd been brought up to believe emotion was weakness. Beckett was taught it was strength. But they both felt it and both expressed it - Artemis in an admittedly more cold and calculated way.
Artemis did care. He just didn't know how to express it. (Beckett didn't really know why.) He didn't really want to be his brother (he was quite happy being himself, thank you very much.)
But Beckett decided there were worse people than Artemis Fowl.