All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
May Allaah reward you generously for your zeal for your religion and your eagerness to guide your parents to what is right. We implore Allaah to help you achieve that and to guide them to that which is good and right.
We have previously mentioned a number of guidelines about the way of offering advice to one's parents who commits acts of disobedience; among those: supplication for them, adhering to patience, wisely and kindly advising them, showing dutifulness towards them, being polite to them, and displaying good manners. Please refer to Fataawa 19274, 65479, 13288 and 5202.
We add here that the advice should not necessarily come from the children; rather, they may seek the help of those whose advice is likely to be accepted by the parents. They can also advise them indirectly by, for instance, playing religious lectures in their presence. The more diverse the means used are, the more likely the parents are to benefit from them. They should also choose a suitable time and circumstance for giving advice in order for it to be accepted.
In principle, the Muslim should hasten to forbid evils and wrongdoings immediately; however, if it is believed that repeating the advice may incur a graver evil like driving the advised person to develop an aversion towards the truth or reject the advice totally, then, in this case, one may adopt a gradual approach in giving advice. Allaah, The Exalted, says (what means): {So remind, if the reminder should benefit.} [Quran 87:9]
As-Sa‘di wrote in his Tafseer (interpretation of the Quran): "The verse means, remind of the Way of Allaah and of His Signs if the reminder should benefit - that is, as long as the reminder is accepted and the preaching heard, whether the whole of the purpose of the reminding or some of it is achieved. The implied meaning of the verse is that if the reminding does not benefit, so that the reminding increases the bad or decreases the good, the reminding is not then commanded but rather prohibited."
Ibn Taymiyyah said: "A wrong is not to be forbidden if it requires a good greater than it to be missed. In fact, to forbid in that case is a matter of obstructing the path of Allaah and an effort to eliminate the obedience of Him and of His Messenger, and to eliminate the doing of good deeds."
You are advised to strive to advise your parents to the best of your ability; Allaah, The Exalted, says (what means): {So fear Allaah as much as you are able...} [Quran 64:16] Allaah, The Exalted, guides whom He pleases to the straight path; therefore, you should not grieve if they are not guided to the Truth. Allaah, The Exalted, says to His Prophet (what means): {Then is one to whom the evil of his deed has been made attractive so he considers it good [like one rightly guided]? For indeed, Allaah sends astray whom He wills and guides whom He wills. So do not let yourself perish over them in regret. Indeed, Allaah is Knowing of what they do.} [Quran 35:8]
Ibn Katheer wrote, "The verse means, 'Do not grieve over them as long as you have delivered the message of Allaah properly; whoever accepts the guidance, it is only for his ownself, and whoever goes astray, he goes astray only for his (own) loss; so you should not be saddened by that." [Tafseer Ibn Katheer]
Finally, we would like to advise you to strive to seek a good husband. You are advised to look for a righteous husband who supports you in your religion. There is no harm in a Muslim woman proposing to a man whom she wishes to marry provided that she adheres to the Islamic norms of conduct, such as covering, modesty, good manners and the like. Please refer to Fatwa 82471.
Allaah Knows best.