British English has these options but American English only tolerates the singular. I always recommend to students that they use the singular because that is always correct everywhere.

Thank you for your question. Just a quick comment, we do have plural nouns like 'people.' But in this case 'family' is singular. That is, it is a singular collective noun. The verb conjugation then requires 's'. All of (the members of) my family always gathers together at my cousin's house for x-mas. My family comes from Scotland. Your family lives in Scotland? All of your family lives here?

It depends whether the group is acting as a group or acting singly. I would say "my family all gather on Christmas Eve" and "my family comes from Scotland". I believe it is true that British English more often recognizes the plural (and is more often correct).

My family lives in

My first reaction when reading those sentences was to say that, "My family all gathers on Christmas Eve." "My family comes from Scotland." were the correct sentences. I think that in the first pair of sentences, both would be acceptable in the United States.