Saw Older Sister Get Taken By Sex Creep (update)

Many who saw my first confession will know what happened.
After writing about what I saw I recently confronted my older sister over what I saw to which she was shocked that I had seen. However, she was not embarrassed over it and said it was more than one time they did it, she apparently also visited him at his university when she said she was going on a work course and she'd be dressed in really low skirts showing off her pawg ass before he'd take her to his dorm to plough her ass and spunk on her cheeks.
Should I tell her husband as they were boyfriend and girlfriend at that time even though it was four years ago now. But she still apparently sends him ass nudes