Yes, it is attainable but generally unlikely. Non-parental custody is governed by chapter 26.10 RCW. http://apps.leg.wa.gov/rcw/default.aspx?cite=26.10. Legally it would be a difficult and complicated process, and you should consult an attorney if you decide to pursue nonparental custody.
Perhaps your parents would agree with you if you explain your concerns.
I admire your desire to protect your siblings from this conflict, but I'm sorry to say this is highly unlikely. Unless your parents agree to voluntarily place your siblings with you temporarily, you would have to go through a nonparental custody proceeding and prove that they are unfit parents. Parental rights are constitutionally protected, so a high burden must be met to overcome them--it is insufficient that the children would be better off with you.
You would need to file a third party custody action and your chances of success are low. Biological parents have an absolute right to determine who sees the children and under what circumstances that occurs if at all.
The information is for general information purposes only. Nothing stated above should be taken as legal advice for any individual case or situation.