As Metatron suggested, you need to write two class scripts, one on the wolf and one on the bird. Then, initialize its properties from the editor. Open up the atmosphere script as an example. Then there is also no need to maintain a separate table for entities, you can simply find any entity by doing FindChild on the scene.
As far as your common methods go, Leadwerks defines several callbacks you can use to run update logic. Take a look here: http://leadwerks.com/wiki/index.php?title=Entities#Callback_Functions Then you don't need to go about defining your own methods. I am not sure they are implemented in Lua though. You can most certainly use them in C/C++.
Before you start re-inventing the wheel, I would suggest you write some small (think Pong, Asteroids, Gorillas) clones to get a feel of what Leadwerks can and can't do. It will save you time later.