So in Hallowverse Sombra was actually the 3rd child born to King Umbrum and Queen Wysteria.
 
He had two older sisters, who sadly did not survive infancy due to complications.
 
The first born  
Name: Whisper  
Race: Crystal pegasus  
Sex: Female  
Special talent: Leading/Guiding others  
CM: A crystal moon drifting through clouds like a ship, guided by a single light.
 
The second born  
Name: Dreamer  
Race: Crystalcorn  
Sex: Female  
Special talent: Illusions/Manipulation of the mind  
CM: An eye symbol trapped in a jewel orb with a crack, representing the mind.
 
Father: Umbrum- fav.me/dciq0u4  
Mother: Wysteria- N/A  
Brother: Sombra