Could somebody confirm my understanding of how this works?

All 3 of the Ynnari units can use this, when any unit (friend or foe) within 7 inches is destroyed and it is only one of the 3 YNNARI units that can make the "Soulburst action".

There is also possibly, an error in the text of the "Index:Xenos 1" on Page 79, concerning the Yncarne. It is not listed as "Infantry", yet it is listed as being able to call upon "Strength from Death".