A soldier returns from war to bury his parents and tend to his sister who remains in a coma. He soon discovers her constant sexual abuse and seeks revenge on her behalf. ~this is a revenge film in the vein of Taken meets Identity~

After losing his parents a [adjective] soldier returns home to care for his comatose sister, only to find out she's been sexually abused for years. Enraged, he hunts down the people who hurt?his?only surviving family member.

Thoughts?

You should start with the sexual abuse.

"When he discovers his comatose sister is being abuses sexually, a vet just returned from the war must..."

Part of what made Taken work was the MC's estrangement from his daughter, so that when he rescues her it also redeems their relationship. Any way you could add that to this logline, like

"A soldier estranged from his family returns home to bury his parents, and seeks revenge after discovering his sister has been sexually abused."

I feel like making her comatose makes it less compelling - sure it's still abuse, but she's unresponsive and therefore not a great character for us to feel empathy for.