Yes, you certainly can make a double batch of this soup in the pressure cooker, as long as the ingredients don't surpass the max fill line inside the pot of the pressure cooker. If they don't, just follow the recipe directions as listed, sautéing the veggies longer if needed until the onions are cooked through and transparent. Otherwise, you don't need to adjust the pressure cooking time on the Instant Pot. It will naturally take longer to bring to pressure and will therefore adjust the total cooking time for you.