When Stefan asked Damon what they were going to do now, Damon's answer was very certain - they were not going to become vampires. Meaning he did not see it as a "good" thing that he wished on either one of them with Katherine out of the picture. And when Stefan showed up as a vampire, Damon seemed pretty much disappointed and sad that he had become one. So yes, he did want Katherine to himself and was made to believe by her that she would be his only but no, he never seemed to want vampirism on his brothers, even when Katherine was out of the picture as he did not regard vampirism as something particularly good -thus his own refusal to become one. Damon wanting Katherine for himself does not mean Damon wished ill on his brother. Likewise, Damon loving Elena and wanting her for himself does not mean he wished ill on his brother and takes joy in him being stuck in the tomb. That is the beauty of Damon and Stefan's relationship. They may fight and quarrel all they like, but they also love one another too much and will always be protective of one another.