Is it obligatory to wear the hijab when speaking with mahram relatives online via audio and video, for fear of devices being hacked by "hackers," especially since the mother gets angry when the hijab is worn in this situation?

If you predominantly expect safety, there is no harm in removing the hijab when speaking with mahrams. However, if you predominantly expect others to eavesdrop and see your image, then it is not permissible for you to remove it. It is recommended to adhere to the hijab as a precaution in times of corruption.