Do you think it would be difficult to add 1 person to an existing party of 3 reservation? My thought is that we will already be occupying at table for 4 for the 3 of us so hoping this will be easy to add. Thoughts?
There should be no problem at all. A party of three is sitting at a table for 4 anyway. In my experience, I've never been told no, even when asking to add several people. If anything, you may need to wait a few minutes after your time.
Not necessarily. Many Disney restaurants have tables that fit 3 only, not 4.
On a previous trip, it was originally set to be myself and my two kids. At last minute, my husband was able to get time off from work, take a flight and surprise us down there. All of our reservations were made for 3. We never had any issue adding him on at time of check in at any of our reservations. In fact, several of the hosts said to me, "of course, and that it wouldn't matter anyway because all tables are square and set up for 2, 4 or larger parties". Round tables are used for larger parties.