Those who conquered the beast sang the song of the Lamb and of whom?

Answer: Moses

Beside a sea of glass mixed with fire, they held harps and sang the song of God's servant Moses and of the Lamb.

“and they sang the song of God’s servant Moses and of the Lamb: “Great and wonderful are Your works, O Lord God Almighty! Just and true are Your ways, O King of the nations!”— Revelation 15:3 (BSB)