Why does 冬休みは家族でイタリアやイギリスへ行きました。 have で instead of と?

Question

Why does this sentence:

冬休みは家族でイタリアやイギリスへ行きました。

have で there instead of と?

Wouldn't "with family" be 家族と?

Answer 1

家族で should be taken as "as a family" rather than "with family"

(Both と and で could be used, though IMHO, 家族で implies that all family members were present whereas 家族と implies you only went with some/maybe all family members.)

Answer 2

Both 家族で and 家族と are correct.

で can sometimes mark an organization/group which makes some action, as if it were a subject.

It's the third definition on デジタル大辞泉.

動作・作用を行う主体となる組織・団体を表す。「政府側―検討中だ」「気象庁―光化学スモッグ警報を発令した」

東京外国語大学言語モジュール treats this as an extension of で as a location marker, as follows:

10　場所を表わす用法の拡張として、主語を場所風に表わすときに用いることがあります。

• 警察で事件を調べています。
• クラスで旅行に出かけました。
• その仕事は自分でやります。

This question is also related:

• で　used for abstract location?

I think it's also possible to think of this as an extension of 1人で, みんなで, 全員で, etc.