What's the Name of That Book??? discussion

Hi I'm trying to remember this book I believe it was the first of a two parter. In it the hero a guy meets with an exiled sorceress from the flying city. I believe she was usurped by her sorceress sister and tries to fight to take it back. I remember she eventually allies with lizardfolk (sexy times in this book) and together they take back the city but the lizards betray her and free some kinda demon from inside the city and start to attack. I had this book something like 15 20 years ago I think. I want to see if it was actually good lol.

The War of Powers; and, The War of Powers, Part 2: Istu Awakened, by Robert E. Vardeman and Victor Milán?

"Fost Longstrider's mission seemed ordinary. He'd been hired to deliver a jug to a wizard on the far side of the forest. Unfortunately the jug contained a sex-starved genie, the wizard was dead by foul means, and Fost was probably the next to die. Then the genie was stolen and spirited away to the City in the Sky. It was up to Fost to steal it back from two beautiful sisters. They were fighting to become queen and, using dark powers, one had called forth a demon. Now Fost's foray was suddenly a terrible war... Now the Princess Moriana has to ally herself with the alien lizard creatures, the Fallen Ones. But their price is the sending of a human volunteer on a Quest that may well be a sacrifice - the seizure of the fabled, death-guarded black diamond called the Heart. And so it happens that mankind's most terrible enemy, the Demon of the Dark Ones, released from a ten-thousand-year bondage, is let loose to rampage and devour across the planet... Princess Moriana plans to raise an army in Medurium and wage war against the Fallen Ones who have captured the Sky City, but the inhabitants of Medurium appear interested only in the pursuit of sensual pleasures... "

Wow well done that's the one. Thanks a bunch it was bugging me. I'm prepared to be disappointed that's it not as good as I remember though. Haha