Invites out and annoyed

Breathe.

Let people get offended that they got cut, that's their problem. You can explain to them that it wasn't an easy decision but cuts had to be made due to circumstances and that you are sorry.

Its possible that invites can get lost in the mail, or depending on where its going it could take awhile.

Have your fiancé reach out and ask if they are planning on bringing all the kids? or if you only addressed and intended to invite Mr & Mrs whoever then have him still reach out and explain with limited seating the kids will not be able to join? Just a simple text or phone call would take right care of it.

My advice is to just try to put all of these details and minor inconveniences out of your mind. You don't need to do anything else related to invites until your due date has passed and you need to contact anyone who hasn't responded. Until then, just live in a world where your invitations and guest list doesn't exist. You will drive yourself nuts if you focus on every little comment from every person in your life.

That's true....you may get several people who will not attend and have extra seats. Freaking out prematurely is added stress

Maybe they are leaving the 7 year old at home?

Stacey said my first thought - maybe they have made arrangements not to bring the seven year old, especially if they are the youngest child. Simply reaching out will solve this - "hi! I got your RSVP and just wanted to confirm, it was only for four." They'll either say, oh, sorry, our mistake, or they'll say "yeah, we figured little Johnny would rather stay at a friend's that night!"

Did you cut the cousin? If not, just say "I'm sorry you haven't received your invitation yet, but rest assured it is in the mail."

As for the friend's mom... honestly, I'm the type that would just send back "?" and let her make an ass out of herself. There are ways to handle disappointment at not being invited, and "what the f%$&" isn't it. That would lead to me being very firm and completely unapologetic. No "I'm sorry, we just couldn't invite everyone--" simply "no, you were not invited. Thanks for reaching out, though!"

I didn't have the same RSVP woes as you are currently dealing with, but the RSVP deadline time was super stressful to me. A bunch of people who never bothered to RSVP, people who would "maybe" bring a guest but weren't sure, and people who weren't even invited telling family members they were considering coming. I know it is hard not to freak out but I promise you will come out the other side. We divided up dealing with all of our RSVP problem people and were able to work through it. We rolled our eyes and vented about it, but tried our best to keep breathing and laughing.