UE4 is a terrible choice for this, while you can technically pose characters in UE4, it is not convenient. That may change a bit in the future as Control Rig rolls out and gets documented but even then, every character in UE4 still has to have a skeleton and be weight painted in some other external program.
Blender will work better but what you should really be using is probably something like Daz Studio. It was designed specifically for tasks like this.