The responsibility of a sister towards her brother before her marriage is, regardless of his age, she should deal with him in a kind treatment, and the relation should be friendly, without any expectations from her brother, because if any accident would take place in the family, such as the father has died, or the husband would die, then that responsibility falls towards the brother. 

Lets say that the your father or husband dies, or a divorce or separation takes place, so all of there responsibilities will fall towards your brother, who will then have to take care of you, and your children, while maintaining his own family life, until you will get re-married, after your waiting period,  during your waiting time your responsibility will fall towards your brother, until you get re-married.  

Or if you are not married, and your father dies, then your brother will have to take care of you until you are married, regardless if he is married or not. Now we should see how you should be kind towards your brother, because the relation is very sensitive, and the responsibilities of him are big towards you, so do not take this relation for granted. If your brother is nice towards you, and looks after your responsibilities, and in return you try to impose your orders on him, or try and control him, and bud in to his personal or family life if he is single, and he is patient, and tries to maintain his relationship between his wife, and you then this means Satan is working on you, and you are earning the anger of Allah, and if you only mind your own business, and thank Allah for a very sweet brother who looks after me, although you are just his sister, and not his child, then you will see an increase in kindness from him towards you, patience and prayer is the key. . 

Today, we see that most families, have so many arguments especially between the brother and the sister, for any small matter. Which eventually leads towards hatred, and if anything would happen to the sister, then her brother will come in the position to take care of her, then because of that Satan will give so many ideas to the brother, about how he use to be treated by his sister in the past, and he will be scared to bring you close to his family, because no one ever wants to disturb his own family life, and if you moved in his family, you make sure that you give so much devotion towards his family, so you are not felt as a burden, but as a blessing from Allah. And stay with patience, and do not say anything to your sister in law, because she is already managing her own family life, don't show that she is an over spender, and has no idea how to manage her house, and how to take care of her kids, or is not looking after your brother properly. Satan gives so many ideas which build a wall between you and them, put yourself in her position, and if your sister-in-law comes and does the same thing while sitting in your house, and does not help in chores, then how would you feel? You are not a guest over there, in that house, for a few days, it is only Allah who know when you will re-marry and move out. Make sure the house does not become hell because of you, it is important to control your tongue, eyes, and your ear, and control your evil thoughts, be optimistic towards them, because after any accident, they are the most immediate towards you, so do not expect them to mold there family life because of you, you have to merge there. 

And you would expect your brother to take care of you, because that is his duty. But if anything is done by force, without love, then the results will be bitter. 

Another important fact to note is that the sister's chest should be covered in front of her brother, or father. In order to respect the manners between the father and her brother. 

The body parts which Allah has asked us to cover, should be covered. Regardless whatever relation that man has with you, except for your husband.

In today's lifestyle it is a very common practice, that we do not care about these matters, because we are under the impression that he is just my brother, father, grandfather, father-in-law, or brother-in-law. These relations are by labels, regardless what age group they are, they are still males. And there should be a distance between the girl and the boy. Regardless of your age, you should not sleep with any male, regardless of his age, or his relation to you, except for your husband.

If you do not have your own private room, you should sleep with a sheet covered over you, from your feet to your neck, with your chest and body fully covered. And try to sleep in the corner, and not in the middle. 

And when you are sitting in a car, make sure your legs do not touch any male. When you sit on a motorcycle, with a male, it should only be your husband. And if you are really young, before the age of puberty, then your father. 

Because Satan, can come in any form, without seeing relation. And his job is to destroy one's family life. Most of the time many accidents happen, but people do not open there mouths, and ignore the matter. Beware of Satan, and make sure you build your self-respect, and modesty in front of any male.

Whenever we talk about guidance, it is general. So please do not look at your brother, or your father with a bad eye, it is important to guard one's modesty only, and should be aware of these matters.