You will need to characterize both the target and source to transfer the motion from a different set of naming conventions to the naming convention of the target rig.
The work flow would be to characterize your target (Rocket-Blueman-UE4-t-Pose) and merge the t-pose file for the Kinnect rig. With the root of the Kinnect rig selected you can then import all of the clips made using the naming convention for that rig and plot all takes to the Character rig and set it’s input to, probably, Character1.
With UE4_Tpose selected you can then set it’s input to Character1 and the rig will snap into position of the Kinnect Character, plot all takes to the target, and once done set input to Character (or what ever you name it).
Once done you can then delete the input character, plot all of the UE4_Tpose takes down to the skeleton and export to UE4 and should work with the default UE4 rig