So if your father is really beating up on your brother who is defenseless (if he is defenseless) absolutely you would do what you can in that moment - without making an enemy in your mind of your father - it's your father's actions in this moment that you are responding to, limiting if necessary, ignoring if possible and safe to do so - not your father the person but his actions - do you see / feel the difference?
Number two, figuring out who can best do what - who is most able to respond in a situation - this takes into account 'responsibility' for that which is real - your father is responsible for his actions, not you, not your mother, not your brother, not anyone or thing in his past. If your brother is attacked and is unable to defend himself and you are capable of defending him, then to a degree... not wholly, but to a degree you would be able to respond. This is no time to lose your presence, or your love though. Right action still and always comes with love, not with fear and not with hatred. If you've read the Peaceful Warrior, you know this.
You know Newton's Laws so you may have a basic understanding of how martial arts work with energy in terms of loving, respectful self and other defense - not attack, or in preparation for attack, but genuine defense - particularly tae kwon do and Aikido - using the energy that already is in motion wisely - diverting or blocking offensive movements and turning them into 'no or little harm' effects and positioning the body to 'meet' energy in motion in a way that allows and creates the least harm to both parties.
It's not for your mind to think about when it isn't happening, it's for your awareness to respond to if and when it happens.
Albeit learning a martial art, also helps to still the mind, increase self discipline, self and other respect and confidence as well as giving the mind and body a positive experience of where our bodies end and another's starts. We fear less when we know our body and mind can respond in a way that we are comfortable with in any situation.
Worrying about if something will happen that is not happening now, is not helpful. Making up bigger and bigger 'enemy' stories about anything in our minds when it is not happening right now, is not helpful.
Honesty is the highest form of love.
Sometimes it is enough to stand in front of a bully and say "No, this is not going to happen.' Other times you do have to apply energy, applying it wisely can be done, can be learned, can be actioned while still being mindful.
So now honestly tell me, did you say this
to increase the 'drama' and the 'poor me' perspective and elicit support for making your father the 'enemy', or is it real - here now real?And how can I help my little brother not to suffer?
Because I just think, if it was real, you would already know the answer because you already would have responded.
We only worry about that which is not real now - that which may have been at one time, or may be in some future time, but if something is happening now, we respond - wisely or blindly - we do respond.
Newton's law says so, doesn't it?