I disliked Kevin because he kept thinking he was cooler than everyone else, and he brags too much. Also, his insults are annoying.
Jimmy is just pathetic. He gets hurt in the most pathetic ways, and he spends too much time with Sarah. He needs to get away from the dolls and tea parties and play some sports. I admit that it's funny whenever he gets hurt, though.
That's because none of the parents ever had some screentime. There were a couple of episodes in which the kids made references to their parents, but we never actually saw them.
Then again, there was that one episode in which Edd had to deliver Ed and Eddy's report cards to their parents. We saw the arm of Ed's aunt(?) and the arm of Eddy's father(?), but not their faces.