What should I do about my unveiled sisters who refuse to wear the hijab despite my reminding them of the Quranic verses, and my parents refuse to impose the hijab on them? And would I be considered a "dayyuth" if I do not intervene forcefully?

Every shepherd is responsible for his flock, and parents must be mindful of this responsibility towards their children. Just as they are keen on their children's worldly benefit, they must also be keen on their salvation from Hellfire. Islam has forbidden ostentatious display (تبرج) and the mixing of women with non-mahram men. A Muslim man would not approve of his wife or female mahrams displaying their allure to strangers. Jealousy (غيرة) is at the core of good morals and faith; the jealous man is contrasted with the 'dayyuth' (one who lacks protective jealousy over his womenfolk), who does not show jealousy over his mahrams. The people of pre-Islamic ignorance (Jahiliyyah) had jealousy deeply ingrained in their souls, so how much more should Muslims? Covering women and safeguarding them helps preserve their chastity, and adherence to the teachings of Islam provides security from fitna (temptation/strife). The father must obligate his wife and daughters to observe the legal hijab and modesty. The questioner is not a 'dayyuth' for disliking what he sees, but he is not permitted to kill. Rather, he should advise his family with gentleness and kindness, and pray for their guidance.