Here are some of the more common verses about incest in the Bible. There are many more, but this is a pretty good start I think.
Lev 20:11 "If a man violates his father by having sex with one of his father's wives, both the man and the woman must be put to death, for they are guilty of a capital offense.
Lev 20:12 "If a man has sex with his daughter-in-law, both must be put to death. They have committed a perverse act and are guilty of a capital offense.
Lev 20:13 "If a man practices homosexuality, having sex with another man as with a woman, both men have committed a detestable act. They must both be put to death, for they are guilty of a capital offense.
Lev 20:14 "If a man marries both a woman and her mother, he has committed a wicked act. The man and both women must be burned to death to wipe out such wickedness from among you.
Lev 20:15 "If a man has sex with an animal, he must be put to death, and the animal must be killed.
Lev 20:16 "If a woman presents herself to a male animal to have intercourse with it, she and the animal must both be put to death. You must kill both, for they are guilty of a capital offense.
Lev 20:17 "If a man marries his sister, the daughter of either his father or his mother, and they have sexual relations, it is a shameful disgrace. They must be publicly cut off from the community. Since the man has violated his sister, he will be punished for his sin.
Lev 20:18 "If a man has sexual relations with a woman during her menstrual period, both of them must be cut off from the community, for together they have exposed the source of her blood flow.
Lev 20:19 "Do not have sexual relations with your aunt, whether your mother's sister or your father's sister. This would dishonor a close relative. Both parties are guilty and will be punished for their sin.
Lev 20:20 If a man has sex with his uncle's wife, he has violated his uncle. Both the man and woman will be punished for their sin, and they will die childless.
Lev 20:21 "If a man marries his brother's wife, it is an act of impurity. He has violated his brother, and the guilty couple will remain childless.
Lev 20:22 "You must keep all My decrees and regulations by putting them into practice; otherwise the land to which I am bringing you as your new home will vomit you out.
Lev 18:5 If you obey My decrees and My regulations, you will find life through them. I am the LORD.
Lev 18:6 "You must never have sexual relations with a close relative, for I am the LORD.
Lev 18:7 "Do not violate your father by having sexual relations with your mother. She is your mother; you must not have sexual relations with her.
Lev 18:8 "Do not have sexual relations with any of your father's wives, for this would violate your father.
Lev 18:9 "Do not have sexual relations with your sister or half sister, whether she is your father's daughter or your mother's daughter, whether she was born into your household or someone else's.
Lev 18:10 "Do not have sexual relations with your granddaughter, whether she is your son's daughter or your daughter's daughter, for this would violate yourself.
Lev 18:11 "Do not have sexual relations with your stepsister, the daughter of any of your father's wives, for she is your sister.
Lev 18:12 "Do not have sexual relations with your father's sister, for she is your father's close relative.
Lev 18:13 "Do not have sexual relations with your mother's sister, for she is your mother's close relative.
Lev 18:14 "Do not violate your uncle, your father's brother, by having sexual relations with his wife, for she is your aunt.
Lev 18:15 "Do not have sexual relations with your daughter-in-law; she is your son's wife, so you must not have sexual relations with her.
Lev 18:16 "Do not have sexual relations with your brother's wife, for this would violate your brother.
Lev 18:17 "Do not have sexual relations with both a woman and her daughter. And do not take her granddaughter, whether her son's daughter or her daughter's daughter, and have sexual relations with her. They are close relatives, and this would be a wicked act.
Lev 18:18 "While your wife is living, do not marry her sister and have sexual relations with her, for they would be rivals.
Lev 18:19 "Do not have sexual relations with a woman during her period of menstrual impurity.
Lev 18:20 "Do not defile yourself by having sexual intercourse with your neighbor's wife.
Lev 18:21 "Do not permit any of your children to be offered as a sacrifice to Molech, for you must not bring shame on the name of your God. I am the LORD.
Lev 18:22 "Do not practice homosexuality, having sex with another man as with a woman. It is a detestable sin.
Lev 18:23 "A man must not defile himself by having sex with an animal. And a woman must not offer herself to a male animal to have intercourse with it. This is a perverse act.
Lev 18:24 "Do not defile yourselves in any of these ways, for the people I am driving out before you have defiled themselves in all these ways.
1 Cor 5:1 It is actually reported that there is immorality among you, and immorality of such a kind as does not exist even among the Gentiles, that someone has his father's wife.
1 Cor 5:2 You have become arrogant and have not mourned instead, so that the one who had done this deed would be removed from your midst.
1 Cor 5:3 For I, on my part, though absent in body but present in spirit, have already judged him who has so committed this, as though I were present.
1 Cor 5:4 In the name of our Lord Jesus, when you are assembled, and I with you in spirit, with the power of our Lord Jesus,
1 Cor 5:5 I have decided to deliver such a one to Satan for the destruction of his flesh, so that his spirit may be saved in the day of the Lord Jesus.
As for Adam.. he was definitely a real person, not an abstract of society or a group of people. How do I know this?
Rom 5:12 Therefore, just as through one man sin entered into the world, and death through sin, and so death spread to all men, because all sinned--
Rom 5:13 for until the Law sin was in the world, but sin is not imputed when there is no law.
Rom 5:14 Nevertheless death reigned from Adam until Moses, even over those who had not sinned in the likeness of the offense of Adam, who is a type of Him who was to come.
Rom 5:15 But the free gift is not like the transgression. For if by the transgression of the one the many died, much more did the grace of God and the gift by the grace of the one Man, Jesus Christ, abound to the many.
Rom 5:16 The gift is not like that which came through the one who sinned; for on the one hand the judgment arose from one transgression resulting in condemnation, but on the other hand the free gift arose from many transgressions resulting in justification.
Rom 5:17 For if by the transgression of the one, death reigned through the one, much more those who receive the abundance of grace and of the gift of righteousness will reign in life through the One, Jesus Christ.
So the question would be... if sin came into the world by Adam (a group of people?) are we saved then by Jesus (a group of people?) No, Adam was a real person like Jesus.
Eve wasn't a previous relative of Adams. She wasn't his sister, daughter, mother, aunt, cousin, etc... she was his wife. They were related in that way.