The first thing that I noticed was that the husband's Sun, Moon, and Mercury all square Pluto. Each of these alone are difficult aspects. The three combined means that aggression and control is central to his core personality (Sun), he has emotional extremes (Moon), and his thoughts (Mercury) gravitate toward aggression.
The husband's Mars (which represents action) is in the 12th House (the secretive House Of Self-Undoing). Even though his Mars is actually very well aspected, its placement in the 12th House could still mean that he carries around repressed rage.
Both his Mars and Sun conjunct his Ascendant, which suggest that he is domineering (Sun's placement) and pushy (Mars placement).
It certainly doesn't justify the husband's horrible behavior towards your sister, but he also has Sun opposition Moon in his chart. The Sun represents the father, the Moon the mother. This suggests that his parents had a tumultuous relationship. He may have learned his abusive behavior from what he observed as a child.
While I understand that it's a difficult decision for your sister as they have a child (and I don't know how Turkish society views divorce), but your sister is dealing with a volatile husband. The husband's 7th House Moon (emotions) opposition 1st House Mercury (thoughts) placement suggests that the volatile relationship will likely continue. The 7th House rules relationships and the 1st House rules the individual's sense of self.