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.
Either two individuals can or they cannot be siblings, or parent and child. There is no in-between (but there can be on a DNA test, but that is a fault with the test and not with the relationship between those two individuals). In our case it is the probability of the event of two individuals being siblings.