I'd expect a sibling called
Omega, nn
Meg.
A British name expert,
Leslie Dunkling, wrote somewhere about the odd spellings he'd found in 19th century records. Most of them could probably be traced back to the parents' regional dialect or personal misunderstanding: Mrrya, for instance, and Alfer. He reasoned that Alfer's parents liked the name
Alf but felt it needed a longer form; perhaps they didn't like
Alfred, or perhaps they'd heard
Alpha used in church and thought that gave it extra dignity. Of course, their spelling let them down.
As for alphabet names in general, aren't they mostly nns for names beginning with the relevant letter?
James Gatsby ->
Jay; and then
Bea for
Beatrice,
Dee for most things (I know a
Dinah who's
Dee),
Effie (OK it's for
Euphemia, but it sounds like a little F),
Gigi,
Elle,
Katherine Theresa -> KT and so on and on. I find them pretty trite, but they do get used. Fiddling around with the names of letters in an alphabet not one's own is an odd thing to do - surely there must be enough genuine names in a language like English without scraping the barrel like that?