Hello,
You might want to consider my 2D Animation Tool called Creature. It does full on Mesh + Bone Skeletal Animation for 2D and a lot more (cloth, hair, dynamics, procedural animation).
It also has a that is integrated well into UE4 pipeline ( Blueprints of course! ) 
Website:
UE4 :
What it can do in UE4 -
Video 1:S01sZY8mTz4
Video 2:
https://www…com/Koh8L03d9-A
Video 3:YxUUaDNPRmo
Cheers!