Children's Books: Oliver and the Dragon

Princess Eliza has been kidnapped by a dragon, and is being held in his cave. The dragon demands the kingdoms crown, so he would become king. If he won't get it in three days, he will eat the princess.
It is only a small kingdom, and all the knights tried to rescue her, but got burned up by the dragon's fire. One of these knights was the older brother of young Oliver.
He wants to avenge his brother and rescue the princess, but he's not a great knight like his brother was. But he wears his old armor, and comes armed with a story.