सर्वे ते all of them, त्वरितं at once, गत्वा went वालि पालिताम् ruled by Vali, किष्किन्धां Kishkinda, वृक्षैरात्मानमावृत्य hiding behind the trees, गहने वने in the dense forest, व्यतिष्ठन् waited

They all at once went to Kishkinda ruled by Vali and there waited hiding behind the trees in the dense forest. Sugriva roars at Vali -- Rama encourages him to challenge Vali, himself hiding behind the tree.