Is what is happening, in terms of obstacles in marriage and work, and his repeatedly seeing one of his female relatives in a dream and her threatening him, due to her?

Marriage difficulties are by the decree of Allah and His destiny. You should examine your relationship with Allah, for sins make matters difficult and ruin hopes, as Ibn al-Qayyim said: "Whoever neglects piety, Allah will make his affairs difficult." Do not worry about your relative's threat, and put your trust in Allah. Sleep dreams may be from inner thoughts or from Satan, so seek refuge in Allah and maintain remembrance (adhkar) and ruqyah al-shariyyah.