In his situation a shotgun was a bad choice. with a handgun or rifle he could of shot the guy.
He had a duck gun. At those ranges the pattern is the size of your fist. Put the bead on the side of the guy's head, away from sister-in-law, and squeeze.
The question is which to shoot first. I'm thinking that the best option is perp without hammer cocked. Or perp with gun on me.
Woman should have folded legs and fell, but this guy wasn't ready to shoot. That is the #1 problem.
“I was lucky in the order.” - William Muny out of Missouri, killer of women and children (As “Little Bill” described him.)
If this guy had small caliber rifle and practiced he could have shot both of the thugs in the eye.