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.
Again, there are duplicates and thie is a huge oversimplification, but you get the general idea. Not only are offspring genetically unique, siblings are also unique even though they both get their DNA from exactly the same source. This is why you can have brothers and sisters that look and act nothing alike.