Even if they are generated during the attack sequence, the attacks do not cause the mortal wounds. In every scenario the abilities cause the mortal wounds. Attacks are not capable of causing mortal wounds directly.
Furthermore, mortal wounds generated during the attack sequence are allocated at the same time as all other wounds from the attack (see core rules). An ability that causes 6 mortal wounds is not 1 packet of 6 wounds, it is 6 packets of 1 wound - since mortal wounds skip the "Save Roll" and "Determine Damage" steps of attacking, it is impossible for mortal wounds to ever be any other way.