What up, MeganeRei?
Aside from the good input Maleth put in there, I think if you were unfortunately approached by some nosy fam 'bout what's in yo' package box, I would tell 'em the truth; that its personal...and just walk away. Its the honest truth because this is a personal and private item that would be inappropriate to share its knowledge amongst family with(other than your mom, since you say she knows already, correct?). I feel that if they think they have the right to ask about this then you should have the right to answer them back (truthfully) the way you see fit.
I fear though, the same thing may happen to me when mine gets here too....But I do try to practice what I preach, so to speak, and will do what I just advised/suggested you to.
Hope it all works out well for the both of us, lol. Best of luck to you, sir! 🙂