Is a Blue-Eyes White Dragon card rare? Because my brother has four of them...

Blue Eyes White Dragon is a strong card,it's rare among finding in one of the Yu-Gi-Oh! card packs but not so rare if someone buys the Kaiba Starter/Structure Deck they give toi a Blue Eyes White Dragon..so in a way yes and in a way no.

In the original series, yes and it is the strongest of all the original cards. But know that there are plus than 1 series now, it's not the strongest among the other series editions.