For a quick solution delete all the bones of your vehicle and just parent all 4 wheel meshes to the car base. Unreal does not require bones with its wheeled vehicle and will take care of it for you. If you are a beginner I recommend that you do not rig a vehicle and export to Unreal since you will face a lot of challenges.
If you would like to continue using your vehicle rig watch this video:
I noticed that the base of both the wheel bones on the left are facing the wrong direction. It is important that you follow the tutorial for proper bone set up for your vehicle. The direction in which the bone are facing is very important.
So your solutions to this are:
1.) Remove the rig and make everything much easier (I highly advise you do this)
2.) Follow the proper rig tutorial and fix your mistakes.
When it comes to solution 2, people face a lot more problems when it comes to the physics of the wheels and it is not recommended that you chose it unless you really know what your doing when it comes to Unreal.
Hope this helps.