The Array Plate was incredibly large, and even with a massive Barlow Flame Demon occupying some space, there was more than enough room for the four companions to sit comfortably.
Unlike the situation on the Iron Ice Plains, the volcano that appeared out of nowhere in front of the Glacial Fortress contained an extremely rich concentration of nature's spiritual energy (to be precise, 'Abyssal Flavor' spiritual energy). Merely coming into contact with the erupting lava could transform a Frost Giant into a demon. That's why Lancelot was able to proceed with the Body Infusion. However, the spiritual energy here, though equally pure, was hardly sufficient for another Body Infusion, although it was enough to maintain his Flame Demon Form.
