Mdtryhht

וְהַיָּמִ֣ים הָאֵ֠לֶּה נִזְכָּרִ֨ים וְנַֽעֲשִׂ֝ים בְּכָל־דּ֣וֹר וָד֗וֹר מִשְׁפָּחָה֙ וּמִשְׁפָּחָ֔ה מְדִינָ֥ה וּמְדִינָ֭ה וְעִיר וָעִיר וִימֵ֞י הַפּוּרִ֣ים הָאֵ֗לֶּה לֹ֤א יַֽעַבְרוּ֙ מִתּ֣וֹךְ הַיְּהוּדִ֔ים וְזִכְרָ֭ם לֹא־יָס֥וּף מִזַּרְעָם: ‏

And these days are remembered and fulfilled in every generation, family by family, country by country and city by city. These days of Purim won't pass away from among the Jews and their remembrance won't vanish from their descendants.

Megillas Esther 9:28

The Gemara derives from משפחה ומשפחה that even Kohanim and Leviyim stop their avodah to hear the megillah, but the pshat of the pasuk would seem to refer to individual families. Rashi takes this approach:

מִשְׁפָּחָה וּמִשְׁפָּחָה. מִתְאַסְּפִין יַחַד וְאוֹכְלִים וְשׁוֹתִים יָחַד. וְכַךְ קִבְּלוּ עֲלֵיהֶם שֶׁיְּמֵי הַפּוּרִים לֹא יַעַבְרוּ: ‏

Families gather together and eat and drink together. And in this way (?) they accepted upon themselves that Purim will never disappear.

It seems that Rashi is saying that the family nature of Purim helps to keep it going. This is something I more associate with other holidays, especially Pesach and Sukkos (and it's particularly clear that celebrating Pesach as a family has kept Judaism alive for many less religious people in America).

My family has always celebrated Purim together, but I've never heard a specific halacha or minhag to this effect. Is there one?

Nit'ei Gavri'el does indeed record the attestation of feasting together with one's family in a number of sources (in Purim 71:4). They are not necessarily attesting the purpose of perpetuation Rashi was explaining, but several are based on Rashi's comments on Ester, M'gila, and Hapardes (Purim 31) no less.

Basically, regarding the obligation to feast, it says "יאכל וישתה בשמחה ובטוב לבב וישמח אנשי ביתו". To corroborate the household aspect, it lists a number of sources, the gist of which is a focus on getting people together, with the specific aspect of those being family members appearing secondary:

• Elya Raba 695:4, citing Seder Hayom: He should gather his household and friends because when a person sits all alone it's impossible to rejoice as needed.




• P'ri M'gadim based on the Rashi in question




• Shibolei Haleket, Purim 21: The feasting happens with family and friends.

Indeed, it provides one source that explicitly equates - as you suggest - the obligation to merrymake jointly in a group on Purim with that on other holidays. (cf. Mishne Sachir II:234)