I’ve had a mental picture of this—it was more death by laser beam than actual fire. But actual fire from God is correct.
However, the men weren’t completely charred, but their tunics remained.
Numbers 10:4 Then Moses called Mishael and Elzaphan, the sons of Uzziel the uncle of Aaron, and said to them, “Come near, carry your brethren from [a]before the sanctuary out of the camp.” 5 So they went near and carried them by their tunics out of the camp, as Moses had said.
One more thing: these were Aaron’s cousins. Aaron was 83 or so at this time so they were likely old and gray-headed, unlike the portrayal of some of the illustrations.