I find it usually works this way:
You are accountable for your own actions, whether they are good our bad. But these actions are your own and no one else's. Meaning when you are a married couple the bad things one person does will not have a effect on the other, but when one half of the couple is doing something good some of that kamai is transfered to the other person.
When doing naam kamai you receive the full benefits for you self, but at the same time some of that will affect the people around you as well (Even if you're not Married). You may not be doing it for them, but small portions of it do reach them in the end. Also when we are praying for another person the benefits are split evenly between you and person you are trying to help. Just like Surban said: