Melt 1/4 cup butter in large skillet over medium heat. Saute onions until tender. Remove from pan. In same skilled, melt another 1/4 cup butter and saute crawfish 5 minutes. Remove from pan. melt remaining 1/4 cup butter and cook shrimp until just pink. Combine all ingredients in slow cooker. Heat on high for about 30 minutes until cream cheese starts to melt. Reduce to low and cook another 30 minutes, or until blended well.