Same-sex marriage, also known as gay marriage, is marriage between people of the same sex, either as a secular civil ceremony or in a religious setting. Same-sex unions are recorded in the history of a number of cultures, but marriage or similarly formalized same-sex unions were rare or nonexistent in other cultures.
DNA between siblings are similar if you share the same biological parents. The genetic information you gain comes from both of your parents, and are a result of fertilization of 2 haploid cells fusing to form a zygote that has a diploid number of chromosomes.
Each sibling gets the same distribution of parental DNA in terms of percentages. That is, each sibling gets half of their DNA from the mother and half from the father*. However, each sibling gets different parts of the two parents' DNA. It always adds up to 50:50, but if you have a gene where the father has the two versions A and a and the mother has the two versions B and b, you could have siblings that end up with AB, Ab, aB, or ab.