This sounds like a dick move, but if somebody tells you to your face that if you do not do a thing, they will murder themselves and it will be your fault, the only correct response is to tell them to go ahead and murder themselves.

Actually, suicidal people typically don't broadcast their suicidal ideations. When people do broadcast them, it's either a cry for help or it is a manipulation tactic.

The cry for help people can be differentiated from the manipulation tactic people by frequency.

People will cry for help a couple of times in their lives. Manipulators will manipulate at every opportunity.

Using a sibling as an additional point of manipulation is another tactic of manipulators.