Romantic and sexual relationships between siblings or other family members is called incest, and if one of the people involved are under the age of consent then it is illegal because its illegal for an adult to date a minor.
Can you marry your own brother?
No person shall marry his or her sibling, parent, grandparent, child, grandchild, stepparent, grandparents spouse, spouses child, spouses grandchild, siblings child or parents sibling. Consensual incest between people 16 years old or more is not a criminal offense.
Can you date your own sibling?
Is it legal to marry your sister? No, it is not legal to marry your sister in any state in the US, or in most countries around the world. It is not legal to marry your sister because a brother and sister share genetic material and this makes the chances of their child having a genetic disorder much higher.