Ptolemy's chapter on parents, in the third book of the Tetrabiblos, sets the pattern the rest of the Western tradition inherited. He does not give the father a house. He gives him two planets, the Sun and Saturn, and reads the father's fortune, standing and length of life from how those two sit in the chart: whether they are free of the malefics, how they stand to the Sun's own light, and whether they rise before or after it.
The pairing is not arbitrary, and its logic becomes visible once the doctrine of sect is in view. Hellenistic astrology sorts the seven planets into a day team and a night team. The Sun, Jupiter and Saturn belong to the day; the Moon, Venus and Mars belong to the night; Mercury takes whichever side it rises with. The father's two significators are the luminary and the outer planet of the day sect. The mother's two, the Moon and Venus, are the luminary and the benefic of the night. The parents are read as a sect pair before they are read as individuals.
That structure does real work in a reading. In a chart born by day the Sun is the stronger of the father's significators and Saturn the harder one. By night the emphasis reverses, and the same Saturn that merely disciplines a day chart's father can weigh heavily on a night chart's. Sect is the first thing a traditional astrologer establishes and the thing a purely modern reading is most likely to omit, which is why one placement can be described as sober authority in one book and as absence in another.