Q.  Can you explain how Cain and his descendants survived the flood?

A. One possibility, Noah's flood was not worldwide. I know what the Bible says. I can't prove this, in fact History isn't my strong point. Pastor Arnold Murray tells us that Chinese history describes the flood around Ararat.

One point to support this is that the dove that Noah sent out found an olive branch. It takes years for an olive tree to grow.

17 And, behold, I, even I, do bring a flood of waters upon the earth, to destroy all flesh, wherein is the breath of life, from under heaven; and every thing that is in the earth shall die.

earth: OT:776
'erets (eh'-rets); from an unused root probably meaning to be firm; the earth (at large, or partitively a land):
KJV - common, country, earth, field, ground, land, natins, way, wilderness, world.

This would give credence to the "local flood" thinking.

In the above verses we can see two possibilities, perhaps even both.

1. The entire globe was not flooded but "the land" where the offence occurred.

2. Beyond saving eight of the Adamic people (Noah and his family), God told Noah to take some of the "all flesh" to keep them alive. All flesh here could very well be the races and even Kenites.

This also clears up one of the "inconsistencies" of the Bible. Where God tells Noah to take two of every living thing and then says to take seven of every living thing. The "by twos" were either unclean animals or Human Beings.

The "sevens" were clean animals, probably for sacrifice and food. Unclean animals can't be sacrificed or eaten by Noah and his family.

Genesis 3:14
14 And the LORD God said unto the serpent, Because thou hast done this, thou art cursed above all cattle, and above every beast of the field; upon thy belly shalt thou go, and dust shalt thou eat all the days of thy life:

Genesis 3:15
15 And I will put enmity between thee and the woman, and between thy seed and her seed; it shall bruise thy head, and thou shalt bruise his heel.

The above verses show that God was talking to the "serpent!" But who was the serpent?:

Revelation 12:9
9 And the great dragon was cast out, that old serpent, called the Devil, and Satan, which deceiveth the whole world: he was cast out into the earth, and his angels were cast out with him.
KJV

19 In the sweat of thy face shalt thou eat bread, till thou return unto the ground; for out of it wast thou taken: for dust thou art, and unto dust shalt thou return.
KJV

5 And I set before the sons of the house of the Rechabites pots full of wine, and cups, and I said unto them, Drink ye wine.

6 But they said, We will drink no wine: for Jonadab the son of Rechab our father commanded us, saying, Ye shall drink no wine, neither ye, nor your sons for ever:

7 Neither shall ye build house, nor sow seed, nor plant vineyard, nor have any: but all your days ye shall dwell in tents; that ye may live many days in the land where ye be strangers.
KJV

33 Ye serpents, ye generation of vipers, how can ye escape the damnation of hell?

34 Wherefore, behold, I send unto you prophets, and wise men, and scribes: and some of them ye shall kill and crucify; and some of them shall ye scourge in your synagogues, and persecute them from city to city:

35 That upon you may come all the righteous blood shed upon the earth, from the blood of righteous Abel unto the blood of Zacharias son of Barachias, whom ye slew between the temple and the altar.
KJV

One needs to know who killed Abel.

In verse 33, the word "generation" should be "offspring", this is a changed word in the Bible. The modern concordance gives the option of using offspring as the meaning of generation. And of course "vipers" refers back to the old serpent of Genesis.

15 Woe unto you, scribes and Pharisees, hypocrites! for ye compass sea and land to make one proselyte, and when he is made, ye make him twofold more the child of hell than yourselves.
KJV