Response to Declines

I think for the first one, a simple "thank you for letting me know" would be good enough.

For the second one, I would let her know you want to keep the ceremony to close friends and family and that you can celebrate after the reception with coffee or dinner.

I think replying by just confirming that you got their reply, and say that you will miss them being there. And for the other one, you could just let them know that the ceremony is for family and close friends only, so unfortunately they can't attend it (due to not being invited lol).

I think you can respond to the first one just Thanks for letting me know, it doesn't have to be formal at all. For the second one if you are ok with her coming to the ceremony then provide the details to her (for the ceremony only, ie time and place) if you are not ok with her coming then like Kelsie said that it is a private ceremony.

I don’t think you have to reply to the RSVP. Since you’re coworkers, you can always mention at work that they’ll be missed.
as for the one who replied maybe to the ceremony; ceremonies used to be open to anyone (at least where I’m from) so even if you didn’t get an invitation, there would be an announcement in the local paper with the ceremony info and people would attend. That’s changed in the last while but maybe this coworker still thinks that’s how it is. If you want the ceremony to only be for those invited, just let her know you appreciate her wanting to come but you were wanting an intimate ceremony and the dance is the bigger celebration for the rest of your friends.

We didn't have a lot of No's (till the week of!!) But we just replied with, "thanks for getting back to us, sorry you'll miss out" lol

For my RSVP's I have only received one that can't make it - and I just didn't reply. If it was an RSVP via mail I wouldn't send a letter back so I don't feel like I should for an email/text.

I like the wording Vinod has mentioned about the response to people who can't come and then for the person who thought she was invited to it all, Kelsie had a great response!

Another way I have said to another person is "You will be missed" nicely. It is nice to respond to them.

At the same time, no answer is needed since you have gotten your reply and confirmed.

I think you can say thanks for letting me know! It’ll let them know you’ve received their RSVP.

Strange, maybe the other coworker assumed her invite was for both? You can either let her know you’re having an intimate ceremony and there will not be space or give her the details. I think it’s up to you and how close you are