There are approximately 1 people working on the game.
As for the engine, I can't comapre it to others as I've never used any others (I'm on a Mac and there aren't many engines that are cross-platform). But the LASSIE engine is pretty easy to get the hang of. The demo was made in what's now referred to as "LASSIE Legacy." That version of the engine is complete and can compile stand alone games for Mac or Windows, but they cannot be played over the web. A new version of the engine, called "LassieAS" is still in development, and it will make Flash-native games (plus have a whole bunch of cool new features that LASSIE Legacy doesn't have.) The final game will be made with the LassieAS engine.
