It would be "mama yako hajambo?"
Why? Because, confusingly, although people ("mtu/watu") are in class M/W, relatives (mother, brother, ...) are in class N/N, and their possessive pronouns take y- in the singular and z- in the plural, just like other nouns in the N/N class:
= your mother/father/sister/computer
= your mothers/fathers/sisters/computers