The most common and most likely answer to this crossword clue is the 8 letter word BRETHREN
I've seen this crossword clue in The Guardian
B
R
E
T
H
R
E
N
More clues leading to the result BRETHREN
Buddy explains!

The straight part
We know that "members of fraternity" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case members of fraternity = brethren.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does BRETHREN mean?
BRETHREN adjective- Of or akin to; related; like
- Son of the same parents as another person.
- A male having at least one parent in common with another (see half-brother, stepbrother).
- A male fellow member of a religious community, church, trades union etc.
- A form of address to a man.
- A black male.
- Somebody, usually male, connected by a common cause or situation.
- Someone who is a peer, whether male or female.