Q. Does a Purim seuda held in a large simcha hall require a mechitza, or is it OK to have people sit together with their families (men and women together)? If a mechitza is required, may one nevertheless attend b’dieved if there will be no mechitza?

A. Horav Shlomo Miller Shlit’a pointed to Rambam (Korban Pesach 1: 11) that a chavura or group eating the Korban Pesach could include as many a fifty people. Since both men and women are ordained to participate and they have to be seating in one place without a mechitza to be considered a single chavura, it would seem that even on a large family Yom Tov meal including guest or neighbors (as the posuk mentions), no mechitza is necessary.
This seems to be today the established tradition in many sheva brochos celebrated on Shabbos or Yom Tov, even when men and women don’t sit together as a family. However, some people usually of a Chassidic background, do place a mechitza.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a