Even without thinking of the Bible, there are so many things we should never think of doing because they do not just seem upright.
It is highly prohibited by God to marry or to have sexual relationships with your kin.
There are some people who are the first, second or third generation of kin to you, you are never allowed to talk to them about anything sexual because those people are family and we God has warned us not to ever involve those set of people in any sexual activity.
I know there are some countries where this is not seen as a big deal but luckily for us here in Nigeria, it is a big deal and no one should ever do that because God is against it. This is not only said through the words of the mouth but also written in a part of the Bible.
Leviticus 18:6-7 says, None of you shall approach to any that is near of kin to him, to uncover their nakedness: I am the LORD.
The nakedness of thy father, or the nakedness of thy mother, shalt thou not uncover: she is thy mother; tgou shalt not uncover her nakedness
If sins can be classified, I will take this as a secondary scene. It is very bad for anyone to involve in anything sexual with his or her family members. While talking about this, know that it should not be your father, mother and siblings alone but has to do with your cousins too.
I know some countries where cousins get married to each other and this is against the will of God. This has to be stopped because it is against the will of God.
God doesn’t want it and mentally it doesn’t speak well of anyone so if you are guilty of this, the Lord wants you to change now!