Are the TNIV and NRSV being too interpretive here? The NLT leaves it as brothers only.

Philippians 4:21 TNIV
Greet all God’s people in Christ Jesus. The brothers and sisters who are with me send greetings.

Philippians 4:21 NRSV
Greet every saint in Christ Jesus. The friends [37] who are with me greet you.
[37] Gk [brothers]

Philippians 4:21 NLT
Give my greetings to each of God’s holy people—all who belong to Christ Jesus. The brothers who are with me send you their greetings.

REB uses colleagues which is probably the least interpretive gender inclusive way of saying it, at least compared to the TNIV. It’s very idiomatic but that’s the translation philosophy.

Paul is explicit in addressing people (every saint, God’s [holy] people), then mentions brothers. How do we know there may have been females with him?

In Colossians (another prison letter) he names names:

Colossians 4:10-14 NLT
Aristarchus, who is in prison with me, sends you his greetings, and so does Mark, Barnabas’s cousin. And as you were instructed before, make Mark welcome if he comes your way.  11  Jesus (the one we call Justus) also sends his greetings. These are the only Jewish Christians among my co-workers; they are working with me here for the Kingdom of God. And what a comfort they have been!  12  Epaphras, from your city, a servant of Christ Jesus, sends you his greetings. He always prays earnestly for you, asking God to make you strong and perfect, fully confident of the whole will of God.  13  I can assure you that he has agonized for you and also for the Christians in Laodicea and Hierapolis.  14  Dear Doctor Luke sends his greetings, and so does Demas.

And also at the end of Philemon.

This has inevitably been brought up before. I came across this as one of the exercises in Greek for the Rest of Us. If you know of other posts or articles let me know.

I had this verse memorized in NIV for a very long time.

As iron sharpens iron,
so one man sharpens another.
Proverbs 27:17 NIV

The guy who helped me become a Christian emphasized that it’s the friction between people that sharpens each other. That never sat well with me.

Then recently I came across Proverbs 17:17:

A friend loves at all times,
and a brother is born for adversity.
Proverbs 17:17 NIV

So having the friction idea in mind I naturally think this means that there will inevitably be adversity between brothers that will help them grow. Again this bothers me. So I looked into it.

NRSV says:
A friend loves at all times,
and kinsfolk are born to share adversity.
Proverbs 17:17 NRSV

and TNIV:
A friend loves at all times,
and a brother is born for a time of adversity.
Proverbs 17:17 TNIV

These express what most commentators would say the Scripture means. Matthew Henry says, “A brother is born to succour a brother or sister in distress, to whom he is joined so closely by nature that he may the more sensibly feel from their burdens, and be the more strongly inclined and engaged, as it were by instinct, to help them.” John Gill says, “and a brother is born for adversity; for a time of adversity, as Jarchi: he is born into the world for this purpose; to sympathize with his brother in distress, to relieve him, comfort and support him;” Adam Clarke says, “A friend loveth at all times – Equally in adversity as in prosperity. And a brother, according to the ties and interests of consanguinity, is born to support and comfort a brother in distress.”

Back to Proverbs 27:17, NRSV says:
Iron sharpens iron, and one person sharpens the wits of another.
Proverbs 27:17 NRSV

The emphasis should be on the sharpening not on the friction. Henry says, “Wise and profitable discourse sharpens men’s wits;”

This isn’t to say that there won’t be friction or adversity between brothers and sisters (in the Lord) and that God wouldn’t use it for our good, but that’s most likely not the primary intent of these verses.