Well here is what happened with the novels:
Capcom developed two light novels in the Devil May Cry universe, written by Shinya Goikeda, illustrated by Shiro Miwa and published by Kadokawa Shoten. Originally released alongside Devil May Cry and Devil May Cry 2 the novels act as preludes, with the epilogue of the novel leading into the opening scene of the game.
Devil May Cry Novel 1 spans from the death of Dante's mother Eva until the beginning of the first Devil May Cry video game. Series creator Hideki Kamiya was able to work closely with Goikeda during the development of the novel, stating that his depiction of Dante and Goikeda's depiction are very similar.
However the events of this novel were contradicted by the events of Devil May Cry 3: Dante's Awakening/Special Edition and the Devil May Cry 3 manga, released years after the novel was published.
In Devil May Cry Novel 2, since the period it is covering is the one right before the opening of Devil May Cry 2 video game, the events may not have been contradicted if a beast named Cerberus had not appeared. And yes it is a three headed dog demon like the one in DMC3. If I remember correctly in the English version of the novel the name was changed on purpose to avoid showing off the obvious resemblance. However that was not enough and Capcom - perhaps also because DMC2 is like it never happened - announced that DMC3: DA/SE also contradicts the DMC2 Novel.
However DMC3 Manga was released and Capcom did not announce anything about it not being canon despite some little mistakes like the meeting between Arkham and Vergil which was shown differently in the manga than what we saw in Special Edition.