To dream of siblings represents an alternative or competing perspective.
Negatively, dreaming of a sibling may reflect unpleasant feelings about yourself losing. Alternatively, it may reflect feelings or beliefs that are counterproductive to your well-being such as insecurity, second guessing yourself, or self-defeating habits. Intentionally being depressed or choosing to lose.
Positively, a sibling may reflect confidence, hope, or someone with more experience than you. A better idea than yours.
If you have more than one sibling than each sibling will represent a competing or alternative aspect of your personality based on the one thing about them that stands out the most.
Your brother or sister may also symbolize your projection of him or her at the current moment.
To dream of a brother or sister that you don't actually have may represent new ideas or new perspectives that compete with your own. They may reflect new feelings of insecurity or self-doubt. Positively, they could reflect a new sense of hope or confidence. A little kid sister may symbolize feelings of responsibility or annoyance.
To dream of a sibling rivalry represents your attempt to overcome your own insecurities or flaws. It may also reflect your struggle to come to terms with alternative opinions or feelings. Alternatively, a sibling rivalry may represent your view of other people competing over different opinions or goals.
Example: A woman kept having dreams of her sister. Her most honest feelings about her sister was the she was always better looking or more popular. In waking she kept having disappointments with dating men who she felt she wasn't good looking enough for. In her dreams her sister reflected situations or comments made by others that made her feel that she wasn't good enough for the men she wanted.
Example 2: A young woman kept having dreams of her brother. Her most honest feeling about her brother was that he was a failure. In waking life she kept having bad luck dating. Her brother in the dreams reflected her own feeling of herself being a failure in relationships.
Example 3: A woman dreamed of seeing her brother. In waking life she was having an argument with her boyfriend and didn't like feeling like she lost the argument.