Of the people, of the people, of the people. -or simply-People, people, people.
le frère de la mère (this is the French correct spelling) is " l'oncle ", the uncle. frere means brother and mere means mother
(the) brother of the mother ( ie oncle - uncle)
litteraly brother of the mother (your uncle, what)
"do" doesn't exist in French, probably "du" (shortened form of de le) is what was meant. Therefore, the phrase is "The mother of the husband or of the wife?"