अन्योन्यगात्रेषु with each other's limbs, विद्धम् piercing, परम् very, द्विगुणम् redoubled, वर्धते remained, तौ those, रणाजिरे in the battlefield, कृतप्रतिकृतान्योन्यम् countering one another and inflicting, कुरुताम् hitting each other

Even though they were piercing one another with limbs, their strength remained doubled in the battlefield. Each of them was countering the other and inflicting and hitting each other.