Reminding guests that only those who Rsvp'd should attend other events

Decline the wedding invite or the invite to the event? If they declined the invite to event wouldn't they not show up anyways? I'm a little confused by the wording of your post.

I assume this is like a welcome dinner before the wedding? I would send out another reminder to make sure whether they are coming. Usually you can add on extra guests 48 hours before the event if your venue is big enough to accomodate all the people that was invited. You can even just call them and ask hey are you guys sure you are not coming. They should know by now what they are doing, as they would have their flight, transport, and accommodations booked. If you already have done that and they said no, then I think you don't need to do that. I am having a destination too, but my events are all mandatory if you are coming to the wedding then you are attending all events.

Also I assume you are close to all your guests if they are flying to Italy for your wedding, and that you have the relationship where you can just call or text as it is really close to your wedding.

What makes you worried that someone who declined an invitation is going to change their mind and just walk in on you?

Just give them one last call. I am sending rsvp reminders to those who haven't responded 40 days straight. If they do not respond, I wont feel bad sending them back home if they show up at the reception venue.

Um, if they declined, then no need. If they failed to RSVP, then maybe send out a reminder that the events are RSVP required if they would like to attend.

I’m also a little confused. Do you mean something like they rsvped yes to the wedding by no to a rehearsal or welcome dinner?