A shield is an essential part to protect the person from external harmful elements during any sadhana. Hence a circular shield was shown during activation.
Thapaadia mai got activated to sense, catch, minute vibrations around her. Her's in White light was for longer time then Shivanand's, who had it for the shortest time. He was doing research since many years in project Amrit. So some of his powers were active. He could survive 24 years of Physical & mental torture in Poland. Nagas tried to change him by Chemical, which his brain couldn't bear it & started getting affected. His Garuda sign is around the place of out of conscious awareness. His thinking will fluctuate between within & out of consciousness awareness. Whenever he'll think as per his noble Garuda nature, the Poison may not affect hm. Only when those thoughts will show corrupted effects he'll change.
Katherine got power of Fire, because her sign is near Manipur chakra in body. Fire is the element of that chakra. Fire is a tremendous form of energy. Her activation time was similar to that of Tiwari & Charlse. Their sign was at the shoulder, near Anahat chakra, the Heart chakra, which is White in colour. They got activation with White light.
These 5 got power based on their speciality. Garuda pramukh got all his chakras activated, systematically because as a leader he needs to consider an overall aspect in his action.
May be Bhairavi is the most powerful among all as she has to bear the wt of the entire Garuda system, she can't afford to let it collapse.