Life threats by brother in law

Dear sir, To start with, my name is Ajay, my sister who is married for the last 10 years is going through a mental and physical abuse by her husband, we tried to intervene on may occasions but was of no use, if fact even me and my family was also threatened by her husband, he also came to kill me with goons and weapons, i was lucky enough to get away and was not hurt , we didnt take any police action at that time, but recently my sister was again beaten up by her husband, very badly that she wass was about to die, we had all the medical reports and police NC, following which he has given written assurance that he he wont repeat the same thing, but of late we came to know that he has started to threaten my sister again, and have started to harass her mentally, not physically though, but my sister is under tremendous pressure form her husband in fact he does not allow her talk to us and visit our home, i have following questions 1: can i still file NC with police for the attack on me in the past (approx three months ago)or its too late 2: can we directly approach police without taking my sister as he confined by her husband in the house, 3 what more evidence should we gather against him to make the case stronger in case we seek divorce