Exegesis:

esontai duo alēthousai epi to auto ‘there will be two women grinding at the same place,’ because the mills are usually operated by two persons.

epi to auto ‘on the same spot,’ hence here ‘together.’

Translation:

Grinding may require the cereal as object, cf. e.g. “grinding corn” (New English Bible), or, the result, cf. e.g. ‘grinding meal’ (Good News Translation, Malay; and Pohnpeian, ‘rub flour’); in Toraja-Sa’dan the verb used is a derivation from ‘meal.’ A common cultural equivalent is ‘to pound rice’ (e.g. in Balinese, Kele). Sometimes a generic rendering is preferable, e.g. because grinding or pounding is not a daily task of women; hence ‘to work’ (Trukese).

Together, or, ‘at the same place,’ may be taken as referring to working the same instrument, e.g. ‘mill’ (The Four Gospels – a New Translation), or, ‘mortar/pounding-block,’ or to working two instruments at the same spot, as is normal e.g. in Shona and Fulah.

Quoted with permission from Reiling, J. and Swellengrebel, J.L. A Handbook on the Gospel of Luke. (UBS Handbook Series). New York: UBS, 1971. For this and other handbooks for translators see here . Make sure to also consult the Handbook on the Gospel of Mark for parallel or similar verses.