Dreaming about cousins signifies familiarity with someone you have just met. The new person may remind them of primary or close childhood relationships allowing you both to relax around each other.
A dream about cousins typically symbolizes a living relative or close friend. The closeness you feel for each other leads to an abundance of hospitality.
Another common interpretation of seeing your cousins in your dreams is that you are letting your guard down. This can be a warning to be careful or it can represent a time in the past where the person felt safe and was able to just be themselves.
The dream is sending the message that you need to maintain a level of skepticism. It could also indicate that there is tension within your family which needs addressing.