If you're doing a 2D-focused game with a top-down perspective, you have come to the right place! Duality is kind of good in handling that.
As far as the MMO part goes, that's where the trouble starts: There is no networking in Duality so far. Although the community prototyped some early network stuff on various occasions, there is no maintained, plug-and-play plugin that you could just use and be done with it. All the netcode will be yours to write.
That said, an MMO is probably not the ideal choice for a first project in general - from my personal experience, the smaller the project, the better. If I may suggest something: Pick a simple concept that all three of you like and know and create a local multiplayer version (shared screen, gamepads) of it. Test it among yourselves, test it with people you know, polish it a lot and put it online somewhere. You'll gain a lot of experience in the process, which is crucial for the next time you start something bigger.
So, if you want to take a closer look at Duality for your project, you'll find a Getting Started
tutorial on the Wiki
, as well as some articles on general engine concepts. There is also the Tutorials
section on the forum, and you can always stop by in the community chat
and say hello or ask for directions