In Acts 6:3, some translations say brethren, some say brothers, and some say brothers and sisters. Which one is correct? Did the men of the congregation chose the seven or was it the whole congregation?
Like many languages, the male gender of words is used when talking about a group of people where the gender of the group is undefined. This is true in both Greek and English, though I'm aware of the attempts of people to change the English language.
The Greek word adelphoi is in the plural masculine form. It can refer to physical brothers (Matthew 12:46), or a spiritual brotherhood, such as fellow countrymen (Acts 13:26) or fellow believers (Acts 15:3). But as I stated earlier the word can be used both for a group of men, a mixed group of men and women, or a group where the gender is not defined. It is the context that has to determine which is the appropriate meaning. For example, in James 2:14-15, "brethren" refers to both male and female Christians.
In this case, notice in Acts 6:5, "And the saying pleased the whole multitude." This makes it clear that it was the entire church, both men and women who were involved in the process of finding deacons for the church.