家母 is a humble (
谦称) form used only when speaking about your own mother to someone outside the family. The pattern
家 + kinship term works for
家父 (my father),
家兄 (my elder brother),
家姐 (my elder sister). Use the matching honorific
令 + term (
令堂 'your mother',
令尊 'your father') to refer respectfully to the listener's family. In casual speech, just say
我妈.