Pretty sure the title needs to be With She Who Likes My Sister to be grammatically correct.
Current title is the official English title, not one that was translated.
Which doesn't actually have anything to do with whether it's correct or not.
The title is grammatically correct, even if it sounds like hell. Which it does.
[I'm] With Her Who Likes My Sister
"Her" is the object in the title, there is no subject. The title we want would be something like Living with a Girl Who's into My Sister