Leaders in the Church at Ephesus
Apollos was an impressive speaker, he was eloquent, knowledgeable, fervent, and bold. Priscilla and her husband Aquila were in a synagogue in Ephesus, one Sabbath, listening to him speak about Jesus, but they noticed something lacking in his message. Apollos did not know about Christian baptism.
Ephesus was a large city, and there was a sizeable Christian community there. Of all the Christians in Ephesus, however, it was Priscilla and Aquila who approached Apollos with the aim of explaining the “way of God” (i.e. theology) to him more accurately (Acts 18:26). That they approached him may well be an indication of the couple’s function as leaders in the Christian community at Ephesus.
Priscilla and Aquila had previously spent a year and half working and ministering alongside the apostle Paul in Corinth (Acts 18:1-3, 11, 18). Then all three had set sail together for Ephesus. Paul left Priscilla and Aquila in Ephesus where they were equipped to minister, having spent so much time watching, listening, and learning first hand from Paul (Acts 18:19 cf. Rom 16:3-5). The couple were well able to teach Apollos who was himself a teacher (Acts 18:25) and an up and coming apostle (cf. 1 Cor. 1:12; 3:4-6, 21-22; 4:6, 9).
Priscilla and Aquila’s Invitation to Apollos
Several English translations of Acts 18:26 state that Priscilla and Aquila invited Apollos into their home (NIV, HCSB, ISV, GWT, WNT). Other translations, however, state that the couple took Apollos aside (ESV, NASB, NET). The Greek verb used here (proslambanō) is commonly used with both meanings “receive into one’s home”  and “take along/aside”.
Considering the culture of hospitality in ancient societies, and the importance of fellowship for the first Christians, I believe the translation that Priscilla and Aquila invited Apollos into their home is the correct one. Accordingly, the early Syriac translation of Acts 18:26 has the couple inviting Apollos “to their own house”. (I strongly doubt that the three held a conversation that took place in the corner of the synagogue or on the side of the road.)
Furthermore, I think it is possible that during his stay with Priscilla and Aquila, Apollos may have been present at a church meeting in their home. Perhaps Christian baptism was one of the topics of discussion and teaching at this meeting.
After experiencing the hospitality and ministry of Priscilla and Aquila, Apollos wanted to keep moving and keep ministering. So the “brothers and sisters”, possibly the members of Priscilla and Aquila’s house church who were now acquainted with Apollos, wrote to the disciples in Archaia asking them to welcome him (Acts 18:27 NIV).
“Grateful to Them”
According to Luke’s description in Acts 18:24-25, Apollos had already been instructed in the way of the Lord when he arrived in Ephesus, and was teaching accurately about Jesus. But with the hospitality, teaching, and the correction offered by Priscilla and Aquila, Apollos now knew the way of the Lord even more accurately.
Apollos and Aquila, as well as Luke who records this story, do not appear to be in any way concerned that Priscilla, a woman, took the lead in ministering to Apollos, a man. That she played a more prominent part is indicated by Priscilla’s name coming before her husband’s in Acts 18:26 (cf. 18:18) in the more reliable, more ancient, Greek manuscripts.
A few years later, Paul would warmly greet his friends who were now leading a house church in Rome. Again, Priscilla is mentioned first:
Greet Priscilla and Aquila, my co-workers in Christ Jesus. They risked their lives for me. Not only I but all the churches of the Gentiles are grateful to them. Greet also the church that meets at their house (Romans 16:3-5 NIV).
Paul did not have a problem with godly women, like Priscilla, being ministers and leaders. Rather, he and many others were grateful for their service.
 Most meetings in synagogues were held on the Sabbath, usually Saturday morning (cf. Paul in Acts 18:4).
 The fact that Priscilla and Aquila spent so much time at Corinth and then set sail for Ephesus from the Corinthian port town of Cenchrea (cf. Acts 18:18), means they probably knew Phoebe, a minister of the church at Cenchrea (Rom. 16:1-2). Priscilla and Aquila probably met Phoebe in Rome, also. More on this here.
 These acronyms stand for the New International Version, Holman Christian Standard Bible, International Standard Bible, God’s Word translation, and the Weymouth New Testament.
 See proslambanō (definition 4) in Walter Bauer’s A Greek-English Lexicon of the New Testament and Other Early Christian Literature, 3rd Edition, revised and edited by F.W Danker, (University of Chicago Press, 2000) 883.
 “Acts 18:26”, John Gill’s Exposition of the Bible, <http://www.biblestudytools.com/commentaries/gills-exposition-of-the-bible/acts-18-26.html>
 See Did Priscilla Teach Apollos? for more on the two Greek verbs behind Apollos’ “teaching” and Priscilla and Aquila’s “teaching”. <http://newlife.id.au/equality-and-gender-issues/did-priscilla-teach-apollos/>
 Priscilla is always mentioned with her husband, but other women ministers, including Phoebe, Euodia and Syntyche, Tryphena and Tryphosa, Persis, and Nympha, are mentioned independently of men in the New Testament.
Did Priscilla Teach Apollos?
The First Century Church and the Ministry of Women
Church Cultures that Include and Exclude Women Leaders
The Prominence of Women in the Cults of Ephesus
Phoebe: A Deacon of the Church at Cenchrea
Paul and Women, in a Nutshell