HarperCollinsCA updated their site with the rest of the parts for Charmed: Let Gorgons be Gorgons.
Each part will have 50 pages for a total of 200 pages.
Preorders for parts 2-4 are not up yet.
The cover(s) have not been revealed yet.
All 4 parts have the same release date (09/29/2015) but that will probably change because they are not planned to be released at the same time.
Let Gorgons Be Gorgons, Part 1: http://www.harpercollins.ca/9781443445986/charmed-let-gorgons-be-gorgons-part-1
Let Gorgons Be Gorgons, Part 2: http://www.harpercollins.ca/9781443448741/charmed-let-gorgons-be-gorgons-part-2
Let Gorgons Be Gorgons, Part 3: http://www.harpercollins.ca/9781443448758/charmed-let-gorgons-be-gorgons-part-3
Let Gorgons Be Gorgons, Part 4: http://www.harpercollins.ca/9781443448765/charmed-let-gorgons-be-gorgons-part-4