What is the ruling regarding the limits of interaction between family members (women and men) in greeting and modest speech, considering that a maternal aunt's sons are like sisters to their maternal aunt's daughters?

The Sharia has set forth regulations for the relationship between a man and a non-mahram woman to prevent temptation, which include: the prohibition of khalwa (private seclusion), shaking hands, and looking at a woman with lust; the prohibition of a woman speaking in a soft, alluring manner; and the obligation of covering the entire 'awra (intimate parts). These regulations apply to every non-mahram man, and the warning intensifies with relatives such as the husband's brother ("al-hamu al-mawt" - the brother-in-law is death). It is permissible to exchange greetings and speak when necessary, and to be in the same place, provided that modesty is observed and there is no private seclusion.