οὗτοι πάντες ἦσαν προσκαρτεροῦντες ὁμοθυμαδὸν τῇ προσευχῇ σὺν γυναιξὶν καὶ Μαριὰμ τῇ μητρὶ τοῦ Ἰησοῦ καὶ σὺν τοῖς ἀδελφοῖς αὐτοῦ
these all were persisting with one mind (in) the prayer with women and Mary the mother of Jesus and with his brothers
There are two common third-declension nouns in this verse, of different sub-groups. Remember that listings of third declension nouns often include the genitive singular form, which points to the correct spelling for the entire declension.
1 ἡ γυνή, γύναικός - woman