It is not permissible for a girl to wear short clothes in front of her parents under any circumstances
Question

                For a very long time, I was unaware that I had to dress modestly around my parents. So I would cover when going out, but at home with just my parents, I would wear pants and short tops. However, I have learnt recently that I should not wear tight fitting clothes around them. My problem is that, because I did not know this for such a long time, the only clothing I have to wear around them sometimes at the moment are the pants and short tops. This is honestly all I have. I have some modest clothing, but my parents do not allow me to wear it at certain times such as when eating, etc. and so I have no choice but to wear the pants and short tops. I am planning to buy some longer tops that will reach down to my knees, but I am completely dependent on my parents and so I cannot go out and buy them immediately. My question is, is it permissible for me to wear the pants and short tops around my parents only, due to necessity, until I can buy some more modest clothing? If it is permissible, should I avoid being around my parents when wearing such clothing as much as possible? This can be difficult as we live together and I would probably have to close myself up in my bedroom sometimes to avoid them. Please reply soon as I am in desperate need of guidance.
Praise be to Allah.
    Firstly: 

    There is no doubt that good behaviour with parents, honouring 
    them and treating them kindly are good deeds for which a person will be 
    rewarded in this world and the hereafter. 

    However, there is no obedience to them if it involves 
    disobedience to Allah and His Messenger, and one should not seek to please 
    them by angering Allah and incurring His wrath, and going against His 
    command and the command of His Messenger.

     Secondly: 

    With regard to what a woman may wear in front of another 
    woman, what is prescribed is for her to cover the area between the hand and 
    ankle, but if a woman needs to roll up her garment for the purpose of work 
    and the like, then she may roll it up to the knee, or if she needs to roll 
    up her sleeves, she may roll them up to the elbow. But she should do that 
    only as much as is necessary; it is not permissible for this to be her usual 
    way of dressing. 

    It is permissible for a woman to cover in front of her 
    mahrams what she may uncover in front of other women; she may uncover her 
    head, neck, foot, hand, forearm, leg and so on. 

    But despite that she should not make her clothes short, 
    coming only to the knee and the like, let alone making it shorter than that. 
    Rather she may uncover only what is ordinarily uncovered of the lower leg, 
    the foot, and the like. 

    She should not wear these tight clothes that show the shape 
    of the ‘awrah or display her charms, even if that is in front of her mahrams. 
    Rather she may only do that with her husband. 

    See the answers to questions no. 
    6569 
    and 
    12371

    What we advise the questioner to do in light of the 
    circumstances that she mentions is the following: 

    -She should try to explain 
    the Islamic rulings to her parents in a proper and clear manner, by telling 
    them about the shar‘i evidence and what the scholars said. She can help 
    herself to do that by using available means such as tapes, lectures, books, 
    fatwas published on trustworthy websites, and the like.

    -She should handle this 
    matter with the utmost gentleness, wisdom and patience, even if that causes 
    her some distress and pressure. 

    -She should try hard to 
    explain the wisdom behind modesty, even at home with her parents, so as to 
    highlight the beauty of Islamic teaching and so that her parents will 
    understand the divine wisdom behind that.

    -She should explain to her 
    parents that the basic principle behind what she is doing is obedience to 
    Allah and to His Messenger (blessings and peace of Allah be upon him), and 
    it is not intended to cause hardship to herself or to make her parents angry 
    with her.

    -She should offer a lot of 
    du‘aa’ (supplication) and turn to Allah, may He be exalted, asking Him to 
    guide her parents, to divert harm and annoyance from her and to enable her 
    to do that which He loves and is pleased with. 

    Moreover, we think that the questioner should try hard to 
    save whatever she can of her personal income so that she can buy clothes 
    that will help her to cover up at home. She does not have to change all of 
    her clothing completely rather in the beginning she may stick to what is 
    absolutely necessary. 

    We suggest that she should have a “prayer suit” or the like 
    that she can put on when any of her mahrams come, if she is wearing 
    something that is not appropriate. 

    And in all of that, she should strive to fear Allah and do 
    her duty towards Him by doing that which He is pleased with and refraining 
    from that which incurs His anger and that He has forbidden, as much as she 
    can, and Allah does not burden any soul with more than it can bear. 

    And Allah knows best.