@Joe Nation,
A sit-down dinner for a Jack and Jill?
How very Noo Yawk.
While I would definitely say adults only, I'd also make sure that the invites are very clear that they're for the recipient of the invite only. Not sure I'd go with Soz's phrasing but I'm all out of nice ways to say things today.
and to be safe, probably only invite 40 - 44 in the first go-round, and give them a short response time so more invites can go out if needed to fill the space.
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separately ... why do some people love baby and engagement and wedding showers/jack and jills/stag and does ... so much?
I don't get it, but they sure are loved by some.