How can my female cousins, who are 18 years old, be encouraged to wear the jilbab, taking into account that they are American and require a special approach in interaction?

You can influence your female cousins to adhere to Allah's command by listening to Islamic tapes, such as those by Sheikh Ali Al-Qarni, Sheikh Muhammad Al-Shinqiti, and Sheikh Khalid Al-Rashid. It is more appropriate for women to invite those like themselves. One must be wary of Iblis's deception, for women are among Satan's most important weapons in leading believers astray, as the Prophet, peace and blessings be upon him, said: "I have not left behind me a trial more harmful to men than women."