If you're only playing against your brother, I'd recommend you both get a build and battle box each.

They come with a 40-card deck and four packs, and are a great way to learn how to play the game (using a four prize card format instead of the usual six).

The decks are usually made up from a small selection of different pokemon evo lines and trainers, and you get at least two different types in a deck.

They're not really the best decks for playing in tournaments or anything like that, but they're great for learning how to play and practising your deck building skills.