Retarget the animations ( tons of tutorials available online for both UE4 and UE5 ) to your full body skeleton, then use them within your ABP using a Layered Blend per Bone node if needed.
If you can’t do it in Unreal, worst case scenario, export all hands animation from Unreal and import them into your DCC ( Maya, Blender ) and create a script that bulk retarget the fingers from the hands animation to your full body skeleton, and export.
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