With the hair done I have started the rig for the alien leader following the same process used in the minion. Nevertheless, for this model I have used Geodesic Voxel binding instead the heat map in order to create a bind with all the elements of the model instead of having to parent them to the joints.
I feel that the process has going faster this time as I have avoided some problems I had rigging the minion model. I
discovered that there is a limit in the amount of influences per bone in order to use the animations in Unreal, there are two limits depending on the final performance as it will take more resources in order to use more influences. A max of 4 for a better performance and a max of 8 as the top number of influences allowed in the engine.
I fixed the problem I had with the head not following the movements of the rest of the body by using a hidden controller that was parented to the neck joint with an orient and point constraint and parented the head controller to this new controller so the head always follow the movement of this controller no matter what.