Makes sense when you remember that the first point of mariage was for children. Whose children is it if there are 4 people in the mariage? The biological parent

Makes sense when you remember that the first point of mariage was for children. Whose children is it if there are 4 people in the mariage? The biological parents? What if the biological parents split up and you end up with only the two remaining non-biological parents. Do they keep the child? If they were all equal as parents except... argh. I give up. My head hurts. I am happy not to be the one who makes laws. This is a very interesting topic.