I have these yu gi oh cards are they good?

First of all, all of the cards with the name Forbidden One in them are very good when combined in a duel, and very rare. Obelisk the Tormentor, Slifer the Sky Dragon, and The Winged Dragon of Ra are what as known as the legendary god cards.(again those are rare and powerful) This probably explains why your best friend's brother would try to steal them. The rest I am not sure of, but all together worth more than 10 bucks. You got a good deal :)