If we made it part of a Multiattack we'd need to tweak the above by replacing the "bonus action" with "multiattack action" and replace Multiattack with.
Right, here's version 6 - I am still getting familiar with 5e. 1e and 2e I knew back to front back in the day (v. rusty now) and have only been playing and more roleplaying than min-maxing at that, in 5e. Getting up to speed - yr suggestions all sound and incorporated..now the thrall....
Did you forgot to tweak in "multiattack action" in the Shrieking Wail or did you decide you preferred it as a bonus action?
It works either way, but I prefer the "multiattack action" version as it prevents them casting spells while wailing.
i.e.:
Shrieking Wail. The pine kindred howls a terrifying dirge. Every humanoid and giant within within 300 feet of the pine kindred that can hear the wail must succeed on a DC 10 Wisdom saving throw or be compelled to flee in panic until the wail ends; acting as if they had failed their save against a
suggestion spell telling them to "run in terror". The kindred must take a
multiattack action on its subsequent turns to continue wailing. It can stop wailing at any time. The wail ends if the kindred is incapacitated. While affected by the wail, a target ignores the wails of other pine kindred. If the target is within 300 feet of the kindred, the target must move on its turn away from the kindred by the most direct route, trying to get as far away as possible. The target tries to circumvent opportunity attacks and obvious damaging terrain, such as lava or a pit. Whenever it takes damage, the target can repeat the saving throw. The target can also repeat the saving throw at the end of each of its turns. If the saving throw is successful, the
suggestion effect ends on it. The
suggestion also ends if the target stops hearing the wail or flees outside ear shot (i.e. more than 300 feet away from the wailing kindred). A target who successfully saves is immune to the wails of any pine kindred with the same or fewer Hit Dice as the kindred they saved against, but can be affected by the shrieking wails of pine kindred with more Hit Dice, such as Thanes or Jarls.