The name Djelibeybi puns on the sweets called Jelly Babies. See also the annotation for p. 109/82 of Soul Music.
It has been remarked that there are quite a few parallels between the country of Djelibeybi and the castle of Gormenghast as described by Mervyn Peake in his Gormenghast trilogy (which we know Terry has read because in Equal Rites he compares Unseen University to Gormenghast, and in Wyrd Sisters he does the same with Lancre Castle). The hero of Gormenghast, Titus, also has a mother with a cat obsession, and his father died because he thought he was an owl. Furthermore, the atmosphere of decay, ancient history and unchanging ritual pervades both Djelibeybi and Gormenghast, with in both cases the presence of arbiters of tradition who are almost as powerful as (or even more so than) the actual ruler.
For those interested in pursuing Gormenghast further (people who have read it almost invariably seem to think it’s a work of genius), the names of the three novels are Titus Groan (1946), Gormenghast (1950) and Titus Alone (1959, revised 1970).