According to Oxford Advanced Learner's Dictionary, relation and relative have the same meaning
A person who is in the same family as somebody else.
I wonder if there are any differences between them. Is is up to me using them in any cases?
Learn English – Relation or relative
word-choiceword-differenceword-usage
Best Answer
In the phrases "any relation" and "no relation", we always use the word "relation".
(We would not say "any relative". It would, however, be correct to say "Is he a relative of yours?" or "not a relative" - though in the latter case, "no relation" is more idiomatic in most contexts.)
In a few expressions, such as "cared for by relatives", it is virtually always "relatives".
Otherwise, the two are synonyms, but "relative" is the more common term.
In "relative by marriage", "close relative", "distant relative", "my relatives", etc, the term "relative" is significantly more common, but "relation" is equally correct. It is also very much more common to refer to "visiting relatives" than "visiting relations".
Of course, there are other (non-family-related) definitions of both words, so they differ in that respect, too.