A Sister-in-law is new to the country and doesn't speak much English. She is convinced that her new family will try and talk her and her husband to get a divorce. So when her husband and mother-in-law are out for the day she goes out to the barn in the very large farm she lives in with her new family and ends up having sex with her father-in-law and brother-in-law. She ends up pregnant with twin girls. Her husband catches his brother getting a DNA test for him and the babies.
Now here is my thought maybe the guy had never actually married the girl and had brought her to the country to marry his brother and she just thought she was marrying the guy who brought her to the country.
Or maybe he did marry her and he divorces her because he knows that she is in love with his brother and she'd really love to be married to the father of her babies. At least he does end up marrying a girl that loves him as much as he loves her. Maybe her sister is his new wife.
And also the father-in-law ends up passing away and giving the farm to his son. He does keep having sex with her until he gets sick and dies.