the basic answer is either use the “Epic” rig with the “Epic” anims
or
use your own rig with your own anims
you’ll never get a good result with re-targeting
the main issue you have is that your character is in the T-Pose , in your 3d programm try and set the character to the same pose as the epic character that will help some, i’ve never bothered trying to re-target the twist bones.