sister in laws or sisters in law Your spouse’s female siblings are not your sister-in-laws, but your sisters-in-law. The same pattern applies to brothers-in-law, fathers-in-law, and mothers-in-law. Facebook Twitter Google + Do you make these 10 mistakes? below table vs table below ect. vs etc. intergrate vs integrate grammer vs grammar skiddish vs skittish absorbtion vs absorption buttox vs buttocks all for not vs all for naught submittal vs submission seam vs seem