I had to read the question over a couple of times to make sure that Dana Matherson was actually included in the character comparison. It is fairly easy to compare the similarities between Roy and Beatrice, but adding in Dana makes it a bit tougher. The difficulty with Dana is that he is the story's antagonist, and he is a caricature of a school bully. He's overweight, aggressive, and dumb as a post.  

Beatrice and Roy do happen to share one of those characteristics. All three characters are aggressive. All three characters will not back down from a challenge. Roy attempts to find Mullet Fingers with a single-minded focus, and then later, in his attempts to save the owls, he is unwilling to give up. Beatrice is even nicknamed "The Bear" because of how rough and tough she can be. She is that way as a result of her rough home life.  

I would also claim that all three characters are somewhat of loners. Roy starts out this way right from the start of the story. He does make friends as the story progresses, but I would never call him a character that could be popular enough to win homecoming king. Beatrice is a self-inflicted loner, because her home life has hardened her, and her focus is always on making sure her brother is safe. Lastly, Dana, too, is a loner, because he is the school bully. He is not Mr. Popular. In fact, most people avoid Dana, because they don't want to get caught in his crosshairs.