Is shunning two unveiled female relatives, boycotting them, not initiating greeting them, and merely returning their greeting with a heavy response considered correct behavior? And is it obligatory to maintain ties with them and advise them to dress modestly? And if so, how can one lower their gaze while interacting with them?

The father of the two girls should be advised and made aware of the immense responsibility he bears towards them and that he will be held accountable for it, in accordance with the Almighty's saying: "Allah instructs you concerning your children," and the Prophet's (peace be upon him) saying: "Each of you is a shepherd and is responsible for his flock." It is permissible to abandon the disobedient person as long as he persists in his disobedience, but the benefit must be considered. If there is a fear that abandoning him will increase his obstinacy, then it must be stopped. The original state, which is connection, should be restored if the disobedient person repents and his condition improves, while observing the regulations of speaking with a young foreign woman. Enjoining good and forbidding evil is a collective obligation (fard kifayah); the sin is lifted from the rest if some undertake it. If there is no fear of temptation and you hope that they will listen to your words and benefit from them, then it is preferable to do so while lowering your gaze.