We will not have an outer/inner envelope - just one envelope. And I still have several months before addressing invites, but this one thing has been on my mind and I figured I'd ask before I forgot about it.
FI's uncle is divorced and has six sons. Four of these sons no longer live with him and do not speak to him or anyone else in the immediate and extended family. FMIL says we need to invite them out of courtesy (which FI is really unhappy about, but I advised him to drop it out of respect for his mother), but she said we should send the invite to FI's uncle because no one knows their address and only the uncle has their phone numbers, and these cousins do not like speaking to their dad or family members. So essentially, we will be inviting "Uncle XX and sons". How would you recommend addressing an invite to seven people?
And this may be a really stupid thought, but: I will be including "__ of _7_ are attending" on the RSVP. If I address it to "The XX Family", I'm nervous that they will invite random people to fill up their 7. Is this even a valid fear? I suppose that, if they're writing unfamiliar names on the RSVP card, FI or FMIL could call the uncle and say that the invitation was intended for him and his sons only.