To dream of your cousin suggests that you haven't been nurturing your natural talents or skills. You should encourage these attributes to grow and reach their potential.
If you dream that your cousin is ignoring you, this implies that you are not recognizing the attribute that is being referred to.
To dream that you or your sibling is in love with a cousin indicates that you recognize and understand the attributes that each of you possess.
If you dream of your actual brother-in-law, consider the situation and the circumstances in the dream. This dream has more to do with every details such as occurrences and events than a visual image of your brother-in-law.
If you currently don't have a brother-in-law but dream that you do or you're the one, it symbolizes your search for family and acceptance.