Double Standards

I dont know how to start this particular post because I am sooo angry and frustrated with my situation/life. I just want to type out all my anger. But I will try to be clear and concise so I make sense but bear with me if I lose focus.
As you are aware I have an exam coming up... I am already stressed about it enough as it is. But home life isnt helping me feel better either.

I have, at present, 2 younger sisters...lets call them spaceman and kofta ( their nicknames as kids). Spaceman is in her 3rd year of Uni and kofta is retaking her GCSEs at college. Now spaceman has exams coming up too so I sympathise. But it is extremely frustrating to see her wake up late and swan out of the house and roll in late in the evening. Slowly, day by day, shes been coming home later and later in the evenings. Last night she came home at 9.30pm.
This isnt just something she does because of studying for exams....this is her all year round. She has zero empathy for anyone in the house. She neglects all her chores at home. She has the nerve to ask for a lift home from the station ( which is only a 5-10 min bus ride straight to our front door). And if you try to talk to her she gives you attitude and rolls her eyes. She does this to mum and dad too, which is so disrespectful.
Kofta is the baby in the family so we tend to be lenient with her. Generally she is well behaved and listens to you and does the jobs you ask her to. But lately shes turning into spaceman. She wakes up late, lounges about in her sleeping suit all day and sits in front of the TV watching music channels or hiding out in her room texting her friends.
Today mum sent me upstairs to revise ( first time ever!), so I gave kofta a list of chores to be done- mainly loading the washing machine, tidy the kitchen n sitting room. To me, this is a small list as I tend to clean up the whole house and cook dinner all by 4pm. Mum went out and I took my nephews to the park with my older sister for an hour or two. I come home and see that kofta has not moved from the sofa since I left her! I was so mad and scolded her and she just stared blankly past me to the TV.
Now I am normally a laid back, tolerant, and patient person. But theres a critical point I reach that makes me so mad with people, including my parents, that I just go into this weird state where I am unresponsive and refuse to talk to people or interact. I refuse to eat food or go out anywhere.
I have stopped trying to talk to my parents about their behaviour because mum just makes excuses and Dad...well hes just given up with them too. It makes me so mad to see how they are allowed to get away with such behaviour. When I was at their age, I never stayed out late. I called my mum to let her know where I was and how long I would be. I would still do my chores even if I had loads of Uni work to do. I never socialised with friends that much as mum didnt approve. And I still done even though Im turning 26 this summer.
Some people might think I am jealous or that I am over exaggerating it but I have spoken to my other sisters ( 1 older & 1 younger than me) and they agree.

At this moment in time I seriously feel like beating the living day lights of both of them for being the worst sisters in the world ever.
But I know there will come a time, where I wont be there to help look after the house or baby sit. I wont be there to clean, tidy, wash, cook, shop. And I will definately wont be there when they need my sisterly help and advice.