<P> A father - in - law is the father of a person's spouse . Two men who are fathers - in - law to each other's children may be called co-fathers - in - law, or, if there are grandchildren, co-grandfathers . </P> <P> A mother - in - law is the mother of a person's spouse . Two women who are mothers - in - law to each other's children may be called co-mothers - in - law, or, if there are grandchildren, co-grandmothers . </P> <P> In comedies, the mother - in - law is sometimes shown as the bane of the husband, who is married to the mother - in - law's daughter . Mothers - in - law are often stereotyped in mother - in - law jokes . </P> <P> Some Australian Aboriginal languages use avoidance speech, so - called "mother - in - law languages", special sub-languages used when in hearing distance of taboo relatives, most commonly the mother - in - law . </P>

What is my brothers father in law to me