Turn the imported character into a rig the whole production reuses. Unreal is the tail of character finalization: it receives the Blender export as a Skeletal Mesh on one canonical skeleton, and you add hand sockets and an IK Rig a single time. From then on, every pose, animation, and shot draws on that one setup. The upstream cleanup is on the Blender Phase 2 page.
The goal is a Skeletal Mesh that every downstream phase can trust: one skeleton, one socket scheme, one retarget rig.
Bring the FBX in via the same FBX import workflow you use for any asset — but as a Skeletal Mesh, and onto one canonical skeleton asset reused across characters rather than letting each import mint its own.
Check that material slots resolved to Material Instances and that import options (LODs, collision where relevant) are sane — ordinary asset hygiene, same as static meshes.
In the Skeleton editor, add a socket on the right-hand bone (e.g. a weapon socket). This socket is the attach point held props snap to in every shot — set it here, use it forever.
Create an IK Rig for the skeleton, defining the retarget chains and goals. It's what lets Phase 4's IK Retargeter map animation from other skeletons onto this character.
On FBX import it's easy to accept a brand-new skeleton per character. Do that and your sockets live on the wrong skeleton and retargeting has nothing shared to map through.
Fix: import every character onto the same skeleton asset. Sockets and the IK Rig then apply across your whole cast.
Skeletal Meshes and sockets get a full lesson in Characters & Animation, and building the IK Rig for retargeting is walked step by step in Retargeting with the IK Retargeter. This page is the pipeline-level map; the asset-import and actor foundations transfer directly.