SOLVED. YA Fantasy - read in late 2010s but likely published earlier. About a child whose uncle dies/goes missing, and they travel to a different universe to find him. [s]

[Percy]

I read this probably around 2016-2019, but it was my father’s so it was likely published in the 80s. It was YA (or possibly adult?)

The book focuses on a teen whose uncle or maybe cousin has died; the uncle lived in an old refurbished school bus, and collected first editions or rare editions of many books. One of these books has a map of a fantasy world, and either that or the uncle’s old diary has instructions for getting to this world, and the main character is convinced that the uncle has gone there rather than dying. They go to this other world to look for the uncle.

That’s all I remember of the plot, but there are a few other details I remember:
The uncle had some sort of fruit or plant name, possibly fig or plum.
The map the main character has is discolored, as it’s not actually from a first edition, so everything in the world looks the wrong color when they travel to it. Someone they run into there complains about something being coral to them when it should by rights be pink.
In this world, things can be created with one’s mind; the main character wills a lemonade into existence, but they don’t focus on the flavor when thinking of it so it’s utterly flavorless.
There’s some sort of oasis or island in it, possible with two palm trees.

[Ayshe]

I think it is searched for from time to time: Figgs & Phantoms maybe?

[Megan]

That one looks a little younger than the one I am referring too. I know they change covers from time to time, but I think this one had real people on it but you couldn't see their faces. Thank you though!

[Kris]

Just to confirm, Figgs & Phantoms (1974) by Ellen Raskin - Ayshe's suggestion - is not your book? Some more cover images - https://www.goodreads.com/work/editio...

Amazon's preview (sample); https://www.amazon.com/Figgs-Phantoms...
- Fifth chapter is titled "Fabulous Figgs Bus."

Wikipedia's plot description:
- "The story centers on Mona Lisa Figg Newton, a teenage girl living in the fictional town of Pineapple with her eccentric family, including: her tap dancing mother, Sister Figg Newton; her uncles, Truman the Human Pretzel, Romulus the Walking Book of Knowledge, Remus the Talking Adding Machine, and Kadota with his Nine Performing Kanines; and her cousin Fido the Second. The only family member Mona gets along with is her uncle Florence, a book dealer. A main concern of the characters is Capri, the Figg family heaven, which involves a ritual passed down through the Figg family for generations. Uncle Florence's greatest wish is to find his Capri. Mona's greatest fear is that her uncle will succeed and leave her alone..."

Kirkus Review:
- "Except for her beloved Uncle Florence Italy Figg, a 4'6" mail order book dealer who with his niece forms the Figg-Newton monster (a stunt that enables them to reach the rare and unusual books on Ebenezer Bargain's top shelf), Mona Lisa Newton has no use for her kooky relatives. (...) for Uncle Flo dies, leaving Mona bereft and more withdrawn now than ever. It is not until she follows him to the imaginary island of Caprichos ("floating through swirling nothingness") that Mona realizes that she has "a lot of remembering to do, a lot of living and learning and loving to do"...

[Percy]

Figgs and phantoms seems like the right book, thank you all! :D