Ok - so you've given them that information. I recommend you stay out of it now. No need to continue communicating with her sister unless it's just pleasantries that have nothing to do with your ex. Her family will deal - or more likely won't deal - with her situation as they see fit.
I know it's tempting, but it's out of your hands now. Your focus should be on moving forward with your life, creating new social connections, building your new future.
