In the following sentence I prefer saying relatives but I am unable to explain why.
It's going to be a small wedding. Only a few friends and relatives have been invited
On doing research I found that both nouns can be collocated after the following adjectives; distant, blood, and close.
We also have the phrase:
Friends and relations 307,000 results
Friends and relatives 1,210,000 results
Judging from the Google Ngram graph below it looks like the former was more commonly used in BrEng and is becoming increasingly rare.
I can't even say that friends and relations is an old fashioned BrEng expression because according to CDO (set at American English) for relation it offers this example of usage:
On our trip, we visited friends and relations on both sides of the family.
In TFD relation is defined thus;
n. 2. The connection of people by blood or marriage; kinship. 3. A person connected to another by blood or marriage; a relative.
Relative n. One related by kinship, common origin, or marriage.
Is there any difference in usage? Are both terms interchangeable? Are relatives and relations, truly synonymous when referring to family members?
EDIT
I would like to expand my question and ask:
- What is the difference between relations and relatives when talking about family?
- Is relations a word that is becoming out-of-date, or as @WS2 commented, is it the "downmarket" version of relatives in BrEng?
- Does the term relatives sound more intimate and meaningful compared to relations as suggested by @Kris?