Where can we meet our friends in FCO Rome airport. They arrive via London. We arrive via Zagreb. We plan to take taxi into town.
You could possibly meet in the the baggage claim area and then proceed to the exit to the ground transportation lobby. Be careful that you don't get scammed by one of the "unofficial" taxis. Many people here recommend Rome Cabs which charge €48 for the trip into Rome (might be a bit extra, depending on how much luggage you've got). This map may help - https://www.lh-travelguide.com/xx/en/rome/fco/#facilities-and-infrastructure-rome-leonardo-da-vinci-fiumicino-airport .
I normally use the Leonardo Express as that's the quickest way into Rome (32 minutes and €14 PP).
When you exit customs through the glass doors in Terminal 3 you go to the left and directly in front of you is a support column with a sign reading, "Meeting Place." That might be a possible strategy. However, you must be in Terminal 3 for this to work.
Buon viaggio,