Snakes can represent the enemy, it can also represent sins and generational curses. Since you were in a barn it is showing your spiritual growth. Are your aunt and cousin believers in God? They can be symbolizing God coming into your life to help you with these snakes and what they represent. Since there were 3 snakes altogether it can be symbolizing the need to use the holy spirit in order to overcome these snakes.
I have a different approach to dreams, that comes from professional psychology instead of Christian symbolism. For my interpretation it would be essential to find out what recent event(s) or concern(s) in your life seem to be related to this dream. There is no obvious symbolism for God in this dream, and the meaning of your aunt and cousin would be colored by your attitudes toward them. What animals were you taking care of in that barn?
Did the barn belong to your family when you were a child? What were your feelings about that barn--wa it a happy time in your childhood? or were there creatures or secret places to be feared?
Initially the 2 snakes were "just curled up together"--so apparently they were not interested in you. But your choice to run for help led to them being separated and a third snake curled up under your chair. None of these tree snakes are threatening you, but their curled force is ready to go into action. In universal (as opposed to Christian) symbolism, they represent the forces of psychospiritual transformation, which is NOT evil or cursed, but would--if it reached into your own being--begin to lift your energy into higher states of being. And this is indeed scary, because growing into higher spiritual capacities means being more responsible for doing the right things in your world.
Normally childhood places in dreams represent your personality as it was formed by interaction within your family of origin. but in this case it's not your childhood home but your childhood barn--perhaps as a symbol of growing up as a farm-kid, but without any specific animals present to symbolize the instinctual aspects of yourself (like dogs or horses). I'd like to know why your helpers are an aunt and cousin--so how would the dream have turned out differently if it had been your mother and another child instead? How does this aunt seem to be different from your mother?
Since these snakes are curled up and doing nothing, perhaps you have recently had events or issues that could be inviting you to develop yourself beyond your present limits. But you don't seem to have the spark in you or know how to get started. So you only know that you are facing some growth challenge, but not how to respond.
Respond please, to comment on both of these interpretations that have been offered to you. You can discuss either or both, or tell either Mrs. Sandman or me what direction you want to take your dream in.