My sister has dumped her boyfriend who's also the father of her two children. The reason why she has dumped him is because he is obviously a psychopath and that is also the reason why i believe she and her children are currently in great danger. I am absolutely shure that this man is planning to hurt her or her children.
There seems to be no clear solution to this problem. Remaining a positive human being, while faced with these threats is a great challenge and i don't mean challenge as a positive thing here.

She should move if she can, leaving the new adress to only trustworthy persons.

Exactly. I'm trying to convince her of this, but she is in a state of denial. It seems to be too terrible for her to fully comprehend that somebody might actually hurt her children.

Honestly, I would just beat the shit out of him.

Some people are so stupid that they only understand violence.... make him understand REAL good.

Get her a taser and some pepper-spray too.

That wouldn't help. She needs to be isolated from him as much as possible. Nothing should trigger "wrong thoughts" inside of him.

I once had a stalker. Had to cut my phone completely and I still get some weird stuff in the mail...after years. So beeing as inaccessible as possible is the only way.

get a restraining order and a mossberg (perfect for home defense)
its a shame theres so many crazy people in this world

a psychopath most likely would not stop if his shit is beaten.

restraining order sounds good, same with moving yet that is a serious effort to replant oneself with 2 kids into a new area.

gun...sounds bad. they say that guns most often kill their owners in a accident. i will never own a gun cause it may not be an accident.

This is one of those rare cases where the police are of use.

Probably the best thing to do is to convince here to contact "Stichting korrelatie". You can call them at 0900-1450 (15cpm) but during workings days you can also chat with them for free.

Also remember that when the need arises she can always contact "Steunpunt Huiselijk Geweld". You can contact them at 0900-1262626. They can probably provide her and her kids a safe haven (safe house) if needed.

That too. Well said.

In fact, the police (in most western countries) can do NOTHING in the case of someone "believing another intends to harm them." Furthermore, being one step removed (the poster believes his sister is in danger, but the sister apparently doesn't), makes the police even less interested (and the courts, too--the poster can't request a restraining order on his sister's behalf).

Back to plan A? Beat him up? Get some pepper-spray?

Violence shouldn't be an option. Besides, firearm are ILLEGAL in The Netherlands (I'm assuming here she lives in The Netherlands) just like pepper-spray and tasers.

Bringing in weapons are plain wrong since there is a good change of the weapon being used AGAINST the victim. The victim is much less willing to use a weapon as opposed to the attacker who's generally very willing to use any weapon available.

Well here in America guns are legal (thank God) and I wouldn't live my life in fear, move, etc.

I'd just shoot him.

Nobody would fuck up my life and make me move and always look over my shoulder, I'd nip that shit in the bud.

Mucho macho talk Miss Coatl

So you shoot him, only to find out he was coming with flowers and the news that he was seeking professional help in the hope things would work out between you two...

I would shoot him if he was ATTACKING me, not just randomly, geeze.

I think pepper spray is a better option than a gun.

I like (and have) both. But I agree, pepper spray is an underated weapon. I use BEAR spray--stuff that comes in a LARGE can, of especially noxious pepper oil content, that's meant to chase off a charging grizzly bear! The stuff is NASTY, and the can is so large I could fend off 4 or 5 attackers if I needed to.

I get mine from UDAP--I think they actually invented what's called "bear spray." There are now others available, as well.

Nevertheless, the very best way to avoid a violent confrontation is to avoid the person who would start it.

Lot's of pepper spray and a mobile phone ALWAYS in the pocket. She can then lock her self in some room and call police if he's trying to attack.
But is your sister capable of defending herself and fight back? Some women can get paralyzed of fear. My wife would probably beat me up with a hammer if I was coming to hurt her or our daughter But generally she's the most loving person I've ever met

A phone is a great idea too.

Phone, restraining order and pepper spray, that is what she needs.