noun
whole family; all the family
Refers to every member of a family together, often used in formal greetings or announcements.
家族一同、皆様のご健康をお祈り申し上げます。
The whole family wishes you good health.
新年のご挨拶を家族一同より申し上げます。
New Year's greetings from all the family.
家族 means 'family' in general, while 家族一同 explicitly means 'the whole family' or 'all members of the family'.
Compound of 家族 (family) and 一同 (all members, everyone).