I can see from your explanation that you and your family are struggling to understand and deal with Jacob's behaviour.
But I can't help feeling sorry for Jacob.
It is clear that he has some psychological issues that need to be addressed, but no one seems willing or even competent to address these issues, with the result that Jacob is falling further and further into confusion and distress, and struggling to find a place in a world that must seem totally against him, as he seems to have no one "on his side".
For the sake of all the family, Jacob needs to be assessed by a psychologist. His problems may be severe, in which case some sort of intervention may be needed. But whether his problems are mild, or severe, it is certain that he will need the support of his family.
With a mother who is willing to flee the country to get away from him, and siblings who are so terrified of him that they cannot bear to be in the house with him, Jacob doesn't have much going for him at the present time.
At least you appear to be concerned about Jacob's wellbeing, even though you are afraid of him. That fear is understandable, and you are to be praised for still worrying enough about Jacob to want to help him.
Please, be insistent to teachers, doctors, any adult who will listen, that Jacob needs help. For Jacob's sake, and for the sake of the whole family.
I wish you well and I hope your teenage years can be more settled in the future.