Expert review regarding the transfer to Unreal engine

We are a small indie company, we have released our first MMO project:

The game has been developed on C4 engine but we would like to transfer the entire project to Unreal. So we were wondering if someone could give an approximate estimate as to how much time the transfer might take, and how many programmers and 3D artists we would need for such amount of work.

Thanks,
Trazzy Team