all one's relatives; kith and kin
A somewhat formal or literary term encompassing both blood relatives and relatives by marriage. Often used in contexts discussing family ties or obligations.
All the relatives gathered to celebrate the New Year.
親族 is a more common, everyday term for 'relatives', while 六親眷属 is a formal, literary expression emphasizing the entirety of one's kin.
親類 is a general term for relatives, less formal than 六親眷属 and without the nuance of including both blood and marriage ties explicitly.
The term originates from Buddhist and classical Chinese texts, where 六親 refers to six categories of close relatives (father, mother, elder brother, younger brother, wife, child) and 眷属 means 'family dependents' or 'household'. The exact derivation is uncertain, but the compound is used in Japanese to mean all of one's relatives.