Ade was able to control red because sunlight and nuturing was the key to having a shadow and soul.
I believe the shadows were able to come out at night because there is no sunlight to control where they can go and then there is nothing tethering them to their person. This is why they killed at night the only plot hole with this is the Jeremiah 11:11 guy but he could have possibly been killed the night before as we have no clue what time they arrived at the beach or when he died exactly.
This would also explain why the son is able to control the red boy in closet (fire gives him a shadow) and on the street in front of the fire. He realized if he focused on the shadow, he could control it