Hello,
It is very common to have problems when using a Riggify rig, it uses it´s own convention and isn´t made for being exported to Unreal.
This script aims to solve the problem:
https://forums.unrealengine.com/community/community-content-tools-and-tutorials/1569172-uefy-script-make-blender-s-rigify-addon-compatible-for-unreal-engine-4
I hope it helps.