What is the theme in Tuck Everlasting?

Immoratlity and related subjects- like Karma ( hinted at with the Wheel analogy) akin to Reincarnation= oddly methinks such super beings would not require food or sleep- right? and why the gunplay. I can"t recall Granny Ryan Clampett toting a shotgun. The immortality plot device is, the Big Gun in the Arsenal- so to speak.