Death of Divinity By Dan Hokstad

Death of Divinity is an epic fantasy that challenges the existence of God and even time itself. Christians, demons, and atheists travel through time, eventually leaving the fate of the universe reeling in the balance.
Book One sees a father transform into a young boy as he journeys back to the Second World War to change the course of history. An evil Nordic entity chases his family through the decades before a modern crusader intervenes, setting up the final conflict in Book Two – Ragnarok. Here, the next generation travels to the Viking era, the future, and into parallel universes, causing a rift between all the gods … and the possible destruction of the cosmos itself.
Ashes to ash to ashes – time annihilates all believers.