General term for a person connected by blood or marriage; often used in legal or formal contexts, but also in everyday speech.
Only relatives were invited to the wedding.
彼は遠くの親族を訪ねて九州へ行った。
He went to Kyushu to visit distant relatives.
Relatives gathered for the memorial service.
I told my relatives about the marriage.
All the relatives celebrated together.
親族 is the formal, often legal term for kin (as in inheritance law), while 親類 is the more everyday word for relatives.
kinship; family relationship