That father is so useless. Reading the story I thought this all happened quickly and the father rushed in to help but this woman was a pro at swinging that knife around.
Then I watch the video and it's some old fat ass tub of shit and the father just looks at her after she had just stabbed his son in the face. Even assuming he didn't realize she had a knife at the time this lady still apparently punched her son in the face, fucking do SOMETHING other than looking at her.
Then when the father finally finds his balls and decides to go after the lady she barely has the strength to slash the knife around so he backs off.
The father should be arrested too for being so damn useless.