If a fandom is your very favorite thing, and you have been dying for fanfiction from it, and you have gone through the trouble of nominating it and requesting it for Yuletide, and your canon consists of only two medium-sized paperbacks, is it really that much trouble to figure out that two of the four characters you nominated actually have full names and/or surnames in canon?
Dita is Perdita Verist: "I'm Perdita Verist, the new teacher, remember?"
Peter is Peter Merrill: "Peter Merrill! How many times have you been told not to climb things at school?" (The speaker is Peter's first grade teacher.)
I did that from memory (verified via Google courtesy of some sketchy outfit that has the full text of the books online), and it has been at least a couple of years since a re-read any of Zenna Henderson's "People" stories.
(I realize that whoever is keeping up this fandom at AO3 is at least as much to blame as the requestor: the tags give them as just Dita (The People) and Peter (The People).