In this video I used the great new 3d scan store free multi expression base mesh - Free Multi Expression Base Mesh
I imported them into Blender setup shape keys and export into unreal engine.
I show you how to export from Blender and import into Unreal then using the level Blueprint and a widget with a slider use an event dispatcher to communicate between the two blueprints. From there the slider can be used in real time to change the morph shape and apply the expressions.
https://dev.epicgames.com/community/learning/tutorials/oZOW/morph-target-using-ui-unreal-engine-blender