The reading order is linear. The next known book is announced for September 7, 2027; the series remains ongoing.
Hachette currently lists this Book as the concluding third volume, on sale September 7, 2027.
Short answers, with sources.
Read Quicksilver first, Brimstone second, then the publisher-listed Fae & Alchemy Book 3 when available. Hachette describes the scope as a trilogy.
Sources: Hachette Book Group — Quicksilver, Hachette Book Group — Brimstone, Hachette Book Group — Fae & Alchemy Book 3
Yes. Hachette identifies Brimstone as the second volume in the Fae & Alchemy trilogy.
Sources: Hachette Book Group — Brimstone
Do not assume so. It is the label Hachette currently uses for the concluding third volume, so Shelf of Worlds preserves that publisher label until a direct source supplies a finalized title.
These sources support the reading order and important details about the books and their editions.