The paterfamilias was head of, and had authority over, the whole household, slave and free, in a way totally unlike a "head of household/father of the family" in any modern, English speaking culture. He was the sole owner of any family estate (even adult sons only received an allowance in his life time) and could disown, sell or even legally kill them; the paterfamilias had the right to decide whether a new born child should be raised in the family or exposed.
That being so, I think it would be preferable to leave the word untranslated.
Women were inferior to men in Latin times, and a materfamilias with the same meaning of a paterfamilias was not even a thing that could be imagined.
Paterfamilias: absolute monarch of the family, with right to give life and death. Always a man, the elder living man of the family (if no husband or father, another man of the family, uncle, cousin, like with the islamic "waliy" (male legal tutor for women, considered underraged forever.)
A grandmother couldn't be the head of the family, and even less the paterfamilias equivalent.