The most common and most likely answer to this crossword clue is the 6 letter word UNCLES
I've seen this crossword clue in The Times
U
N
C
L
E
S
Buddy explains!

The straight part
We know that "Relatives" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case relatives = uncles.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 UNCLES mean?
UNCLES noun- The brother or brother-in-law of one’s parent.
- The male cousin of one’s parent.
- A companion to one's (usually unmarried) mother.
- A source of advice, encouragement, or help.
- A pawnbroker.
- An affectionate term for a man of an older generation than oneself, especially a friend of one's parents, by means of fictive kin.
- An older male African-American person.
- To address somebody by the term uncle.
- To act like, or as, an uncle.