Please add some details about the nature of bullying any why the 24-year old is not able to defend themselves. Otherwise the question may be closed as being too broad.

@user61034 The bullying is physically abusing, hitting and hurting the older one. The age difference means that violence is prohibited. I wrote this on the question

Are you completely against physical responses? And are we talking about a male or female 14yo? (You don’t have to answer the second question, if you’d rather not.)

@Stephie We are talking about a female 14yo but I would like to get a more general answer that would hold for both sexes. I am unreservedly questioning the pedagogical value of physical responses. I am categorically skeptical. I could aprove of physical responses only as long as their pedegogical value is reasoned and explained. I am afraid that even if the behaviour were to be prevented( I am also questioning the very preventivity of physical responses in itself) the person would only abstain because of the fear of punishment without earnesty understanding the reason for punishment.

The 24 year old is entitled to reasonable self-defence against an assault, just as they would be when attacked by a stranger in the street.

@PaulJohnson Self-defense is limited to when the attack is present or when the danger is imminent(when even the least delay probabilistically but inevitably leads to harm). There is no self-defense after the attack already took place(even if the counterattack is only 1 nanosecond later). Self-defense aims at stoping a current attack and not punishing or preventing a future attack. The 24 year old is not entitled to punishing their younger sibling likewise they are not entitled to punish themselves a stanger in the street(after the attack they are only allowed to arrest and drag to the police).

@GeorgeNtoulos Your original post said "The older one can't really defend themselves because of the age difference". They can. I agree that physical discipline is a separate matter. For that they would have whatever rights you chose to delegate to them (which would of course have to be legal under your local child protection laws).

If you won't allow self-defense over legal technicalities, have you considered calling in the heavy artillery, i.e. calling the police? Assault is assault, be it between siblings or strangers. Assault is a crime.` It's illegal and getting the police involved should meet with your legally inclined position.

@anongoodnurse Parents have the right to discipline by law. A right noone else has. You can scold your child without any legal problems try scolding another person's child instead. If the Law gives a right it is probably because it is different to be disciplined by your parents and different to be disciplined by the police. Parental discipline is supposed to have a greater pedagogical value. There are some things you can only be taught by your parents(socio-affective parents) because of the quality and quantity of the time spent with them.

@anongoodnurse Parenting is a functional right. It is both a right and a duty. If my child commits a crime my parenting is questioned. The onus of parenting is on me and not on the police. Otherwise I risk getting parenting removed from me or some other sanction. Discipline is both a right and a duty. I just can't think of how to discipline and punish.

@anongoodnurse How can the older sibling "defend" themselves at the moment or after( not before) they get thrown a chess piece or any other piece of some game, they get insecticide or repellent sprayed on their face, they get spat on their face. These hits are unexpected and for "fun"(some really disturbing fun) and there is no barrage or flurry of attacks. 1 attack happens and finishes there is no imminent danger to defend themselves from. The issue is more general. It is bullying and not just a specific amount of incidents. The older sibling can expect future attacks but none is iminent.

You already list a number of options you don't like. Why do you find them poor?

@hkBst I don't know if I should add the details to the question as it might be a wall of text. I do not like physical responses because they are the ultimum refugium the last resost. They are not a sanction or a punishment to levy when the attack takes place or after they already took place they are a privilage to stop or prevent a present attack during its occurence or when the danger is imminent. Physical responses signal urgency to me and they are aimed at the present or the imediate future not even a couple of minutes after the attack(the specif instance) finished,

@hkBst I don't like forcing a positive action. It seems like forced labour. Children servise is a parental right it should not be levied as a punishment. It should not be linked with negative connotations. I don't like confiscating electronics because they need the means to communicate( have lessons) and because I don't want them to link electronics with something good. I am afraid of addictions. I don't like confiscating they property either just because it is a constitutional liberty.

"The onus of parenting is on me and not on the police. Otherwise I risk getting parenting removed from me or some other sanction." Spraying someone in the face with an insecticide is a crime; the potential for organophospate poisoning is not to be taken lightly. Maybe outside forces are what is called for since clearly you are not able to instill responsibility into your youngest and are stumped by consequences. Your concern should be for the protection of the innocent, not some sanction against you.

@anongoodnurse There has never been an escalation after talk-downs failed, there has been no attempt to instill responsibility in any other way but begging and imploring. An escalation is indeed absolutely needed. These incidents were taken lightly before. The police would sanction only the parents and not the 14yo. I can easily see the 14yo continuing the "fun" even if their parents get punished. It was their parents and not themselves who got punished. The motimation to escalate is there. The police would only motivate the parents to punish their children instead of punishing themselves.

Begging and imploring are not parenting. You are the core issue as you routinely state how you avoid using your power to both protect the innocent and discipline the aggressor. Power and HOW you wield it are critical components of effective parenting. I dont know why you frown on it, but you abdication of exerting control specifically from the power of your role as the parent is the reason there is a problem.

@AdamHeeg Does confiscating electronics intensify the tendency to get addicted in them? How to confiscate electronics when they need them to communicate and have lessons during quarantine? abc.net.au/news/2017-10-27/… If chores are given out as punishment as opposed to a rightful duty/obligation( Family Law itself says children must help proportionally to their capacity) will children become inclined to refuse to help( by doing chores) their parents unless it is given as a punishment?

@GeorgeNtoulos My goal is to avoid seeing you back on here in 8 years asking how you can rebuild a relationship with a then adult child who is in and out of jail and can't hold a job due to the inability to emote with others and place those around them in a high enough regard to treat them safely and respectfully. You continue to make intellectual arguments while your house is falling around you. Your intellectual arguments against taking control are a modern day 'emperor's new clothes' situation. I'll continue below.

@GeorgeNtoulos Your 14 year old is exhibiting behaviors that will result in being arrested. More importantly, they are demonstrating complete disregard for social norms, the safety and health of those around them, and in the long run if you don't take control then a police officer will (later when this behavior continues as an adult). The fact is that if you don't teach this young person some important life lessons then society will. Society teaches these lessons by loss of jobs, fines, imprisonment, and other legal issues. You avoiding teaching this lesson will only harm them later.