The book in question is an older British book, I remember finding it around the mid-to-late 90s, about a young boy being raised by his “aunt” (I clearly remember that she loved taking baths with the Purple People Eater fragrance, which was used later in the book by a sewer-comber who knew where her house was because of the smell) who is approached by a young witch who thinks she’s an outcast because she isn’t ugly, whose name is Gherkin, along with a few other strange characters – including an animal from the island each of them is from that looks like a soft white seal, loves music more than anything, and emits a thick fog when happy. The boy is the lost son of the king and queen of the island, and is the only one who can help save them from some calamity.