Address dilemma

I would reach out to FHs family that you do have addresses for. Start with your future in-laws, they may have most, if not all, of the addresses you need. That's what we did. My FHs mom gave us most of the addresses on his side of the family.

If not the in-laws, maybe there is someone else in the family (aunt, grandma, etc.) who can help you with some of them.

Other than that, I don't know. Reaching out on Facebook is a good idea, for those that have a profile.

Definitely try through other family members. Not sure how you reached out via Facebook, but it seems like now you can message someone even if you're not their friend. That's great, but it often doesn't actually notify the person. I've both sent and received messages to someone I'm not friends with, and sometimes you don't notice it until you happen to open the message tab. That being said, you might want to try to actually add them as a friend to make sure they see your message.

I'd send out all your other invitations now, so people have at least 1 month to RSVP. Then ask your fiance & his parents/siblings to reach out to the 10-15 people you need and just send those later.

That's what I was considering too. I'll talk to FH today and see what he thinks! Thank you!

Honestly, if you don't get a response from them, don't invite them. You've already reached out, so there's not much else to do if they don't reply!