At first, Huck's main reaction to the feud is confusion. He doesn't understand the reasons for the feud and the continued killing back and forth between the Grangerfords and the Shepherdsons, and doesn't really agree that the fighting is justified after Buck explains the history of the conflict.
Huck is upset to awaken and find that Buck and the others have left to chase down Miss Sophia and Harney without him, so hurries to catch up with the clan. Huck's hiding place up the tree allows him to talk with Buck and learn of the deaths on both sides. Huck is able to watch the next round of fighting while remaining unnoticed himself, which means he witnesses the Shepherdsons shooting Buck and his cousin Joe.
At the end of the day, Huck regrets having helped Miss Sophia and not telling Col. Grangerford about the note in the Bible, is deeply saddened and sickened by the death of the two boys, and is relieved to return to his "family" of Jim and the raft.