Gender reveal party

Km • 27. Married 5 years. Our daughter Stella Claire is our entire world. Born Nov 15. 2015. Pregnant with #2 due in April.
Hubby and I want to do a GR party in July. Problem is our families are huge -- with kids were looking at 40 people! That's including grandparents, aunts, cousins, their boyfriends etc. Part of me just wants to do immediate family but this is the first baby/grandbaby and everyone is so excited. And how does that work? Do we text/call everyone who wasn't invited and tell them? Let Facebook announce? We're so lost and don't want to leave anyone out. Thoughts? Insight?