Interesting, I am faced with a similar situation, except I am the mother and I consult with my 19 year old son.
Warning: there is no easy solution and to create a change takes consistent and extended more effort
I have three children:
Two sons, 19 and 13.
A daughter 12.
Their father died 10 years ago, so no father.
I have been going through this with both younger children, more so my 13 year old son, but as he plays up, so does his sister (case of monkey see monkey do ;-)
Firstly I will relate my experiences with my 13 yo son then move onto my daughter (as I have found they need to be managed differently).
13 yo son
My 13 yo son came home with the worse school report card, ever. Even he was ashamed of it, and it's "cool" for his bunch of friends to do no work. He was raging at every boundary I would make. Swearing, damaging things and wouldn't listen. He wanted to be homeschooled (he hated starting high school), was on facebook chat, was playing online games and chatting to people for hours, started a youtube account and uploading videos, and so on.
- first defence, electronic bans. I installed family safety on all our electronic devices. I, temporarily, closed his facebook account, I permanently closed hi youtube account. He has no access to online gaming. This I did over some months. If he didn't do his chores, was rude, swearing, aggressive, he lost all internet privileges, except the urls needed for homework. He would earn time and url access with good behaviour.
His behaviour has improved I am buying him more credit for his mobile phone, but paying the extra for smart controls, so I can create a blacklist and whitelist for incoming and outgoing calls.
second defence, social bans. I regard this as a more severe and less preferred punishment, as I believe my children's social networks are important for their emotional health and development. I have only banned one of my son's friends from his life.
third defence, positive activity. My oldest (19 yo) son teaches and trains martial arts for a living. He has asked me to bring his brother in 6 days a week for training, twice a day in the school holidays. This has been brilliant for filling the void created by removing counter-productive activities. It has helped instilled discipline, he has the role models of older males and it is physically active, and so tires him out and a great release of aggression.
12 yo daughter
Now my daughter is a little trickier, as her needs are not in such great accord as the two boys. However, she still craves time with and the attention and approval of her eldest brother (contrary to her transient protestations).
Basically I have followed the same principles with her as with my younger son. The differences being:
She doesn't do as much martial art training, as she is younger, and so unable to do the adult classes. In this time I have offered her coaching with her homework, or some mummy daughter time.
I have not banned her socially, as she had a tendency to be socially isolated, except for the influence of one friend. An older girl, who had attitude, plus, plus. I noticed her attitude and behaviour deteriorating when she was in touch with this girl. She was identifying with the "older" girl and trying to behave "grown up". I have carefully steered her away from the "popular" girls over the past few years and, successfully, encouraged her to mix with a group of girls who are a little more innocent.
We will "window shop" online. However, I buy her clothes online, when she is not home. This way I know what she likes, but can maintain a manageable dress code, as the girls want to mimic the older girls and wear clothes, I believe, are too "sexual" for this age group.. (and in fact any age group). It's a hard knack at trying to sell this angle to a young teenage girl, I know, but worth the perseverance.
She gets very emotional and when she gets into a state, cannot be reasoned with. So I wait until she is calm and then chat with her. I also try to implement cause and effect consequence type punishments. Example: If her room is a disaster and such a mess, I cannot discern clean washing from dirty, and she has not put her uniform in the laundry (even though I have asked several times); she is faced with going to school on a Monday in a dirty uniform, that she has to spray with deodorant. This happened twice. She now has a tidy room.
If she gets worked up because her hair is not "perfect", I give her warnings, we are leaving in x minutes, and count it down. Ok we are leaving now. She'll scream and come in tow, but I explain to her, she needs to manage her time and sometimes accept that ripping out her hair bands and restyling her hair several times over a perceived imperfection, may not be a prudent use of time.
I am hoping you can use some of these. It will not be easy. It is easier than having increasingly hormonal teenagers becoming delinquent. It is important you and your mother are in accord on all matters. Do not disagree in front of your sister. My son and I discuss things privately. I keep him posted and he is calm and, luckily for us, an exceptional role model.
Almost forgot. They must have completed homework to earn electronic privileges, and if they don't manage their homework, I don't bail them out, they have to wear the consequences of trouble at school. I do offer to help them, but they know they cannot ask me the night before, and if it's a project, they need to give me minimum, a weeks notice.
The best advice he gave me, was this:
Mum, I tell them to do things and they can't argue with me, because I'm doing it also.