How can one invite people to Islam and convince relatives of it, especially those who believe in God alone but do not adhere to the teachings of the religion, such as the hijab?

The optimal way to invite the questioner's husband's aunt and her friends to Islam lies in a series of steps, beginning with an introduction to Allah Almighty and His attributes, followed by an introduction to the divine messages and humanity's need for them. This is succeeded by an introduction to the Holy Quran as the final message, and finally, an introduction to the Prophet Muhammad, peace be upon him, and his biography. This should be presented in a manner suitable for the invitee's situation, with the possibility of utilizing specialized books on Islamic creed and providing translated copies of the Holy Quran. As for the issue of hijab (definition), it is a consequence of accepting Islam, and its wisdom becomes apparent through the pursuit of safeguarding honor and purifying societies.