Layer1 keeps the deform bones (all of them are required). Layer2 keeps IK bones and twist bones. You can ignore the IK bones (they don’t get any weight and are just helpers). But you have to take care about the twist bones:
Otherwise you would get something like this: Re-tarjet problem and please advise - Character & Animation - Epic Developer Community Forums
The finger-bones in the last screenshot are a bit off from the mesh? Otherwise it looks like a UE4 similar pose. Is this the rest-pose (if you select the mesh and enter edit mode … does it change the pose)?