Blue Ruin
(2013)

Dwight (Macon Blair) learns that Wade Jr. Cleland did not murder his parents. The real killer was Wade Cleland Sr. Wade Sr. was angry that Dwight's father was having an affair with his wife and decided to kill him; Dwight's mother was collateral damage. Wade Sr. had terminal cancer and the family didn't want him to die in prison so the family convinced Wade Jr. to take the blame.

In the end, Dwight breaks into the Cleland residence and finds all their guns and throws them in a nearby river. He leaves them a message on the answer machine and lies in wait. When Carl (Brent Wezner), Hope (Stacy Rock) and Kris (Eve Plumb) return, Dwight watches them listen to it and hesitates shooting them. But when Carl threatens his sister's life, Dwight shoots him dead. As he holds the other two at gunpoint, William Cleland (David W. Thompson) shoots Dwight in the chest with a shotgun.

Kris urges him to finish Dwight but William doesn't want to. Dwight tells him his wound is probably mortal and he can leave now and take his car. Hope motions to William to leave and he exits the house. Dwight tells the two women that he knows that William is his half brother and how stupid it is that because his father loved their mother, everyone had to die. Kris reaches under a chair for a gun Dwight missed while Hope charges him. The gunfire spray accidentally  shoots Hope in the head while Dwight returns fire.

All three are killed; Dwight in his last moments believing that he made a mistake in letting William go, thinking he will still go after his sister. However, unknown to him, William sees the gunfire, and believing the whole feud was pointless (and that Dwight had just cause to go after them) drops the shotgun and walks off, apparently willing to leave Dwight's sister and her children alone.

Thanks Spectre!