That's horrible to witness.
I'm a religious Catholic. This may be a case of demonic possession, which is terrifying, and fortunately very rare.
If you think that's nonsense, read the definitive book Hostage to the Devil by the very brilliant Roman Catholic priest Malachi Martin:
No matter how skeptical you may be, if you actually read that serious book, you might be more open in your thinking. And that might be important for you and your family.