I want to make games like this.
simple 2d graphics but using Red Dwarf server on the background.
what flash game engine should I use ?
You seem to be under the opinion that an engine will allow you to make an MMORPG straight away. Read this, and rethink your idea.
You could probably use Flixel or FlashPunk for the engine itself. Then have fun spending a few years dealing with the networking and all the content you need.