Why where my older half sister and older brother such jerks too me

when I was in 6th grade my sister would pull my hair scream in my face hit me and call me names as well as my brother who pushed me down and said I was"ugly as hell".my elder half sister can't be jealous she is vain and narcissistic about her looks and my dad(her step day)favors her and spoils,worships her and my mother divorced him but loves her only.now she is asking me to forgive her(i honestly haven't yet I still resent her)
nobody at school truly cared for or liked me I was bullied they were both popular almost every guy drooled over her and almost all the girls practicly threw themselves at him.but almost everyone called me ugly and some told me I was beautiful I am insecure about my looks but confident in my personality.i am a 17 year old girl with thick eyelashes azure blue eyes with a dark blue ring around my irises and a splash of green near my pupil .i have thick dark brown hair a oval shaped face and two beauty marks on my face one above my right upper lip one above my right eyebrow my skin is almost a porcelain color I weigh from 111-118*switches every now and then*.my dad now expects me to be kind and caring ever since her separation*she had phone sex with some guy and he(her husband) caught her*and wants me to spend time with them(when I wanted to kill myself*almost did*NOBODY was around me ever to watch me or care for me.now I don't honestly care for them they wronged me when I looked up to them loved and appreciated them now I am cold and sadistic to them I dont care if they live or die and never will it hurt cause they were my own flesh and blood and my dad said he would disown me if I hurt them I am going to possibly dis own him cause of her*elder sister*cause he loved her more I wanted us too be equal in love.he wanted to put me in an insane asylum and called me useless and lazy and practicly pathetic he and brother said it was sister who had it worse cause she was called ugly for about 2 year cause of her eyebrows and now she is a whore who sent dirty pics to some guy and had sex with 11 different guys I on the other hand never had a boyfriend LOATH my looks never kissed a boy and i'm a virgin.my elder siblings both were trouble makers both were sex,drug and alcohol addicts iv been drunk once dont want to die*drugs are bad and I dont need to lose anymore brain cells)and again in a virgin...but why is my sister and brother assholes to me same with my dad who said I make him happy*no its that cock-hawing half sister of mine that makes you happy*...i do love my siblings but I will NEVER forgive them

You sound like a very pretty girl I can assure you. I don't know their reason for being such jerks because there could be many such as jealousy. I think it's your choice to forgive them because blood isn't always thicker than water which I know from personal experience but don't forgive them if you're not ready. No matter what don't kill yourself, it may sound cheesy but you've got plenty more to live for and you shouldn't give in; you need to show your dad and everyone else that you are a great person and nothing that they say can change that.
What I recommend is to try to be positive and surround your self with people that love and appreciate you, that's what I'm currently doing and it honestly makes me a lot happier and when you feel down and you don't have any friends to look after you at that moment in time, distract yourself with books, homework ect. Also any time that you think anything negative just try to think positive with compliments about yourself.
If being this cold person you're supposed to be effects your social life and stops you from making friends just talk to people in you class even if you don't know them that well, bring up a band you like and hopefully you'll make friends.