Hi Xeny, the answer of your question are in these post,
Looking for COLLABORATION BETWEEN TEAM to achieve GAMES and talk about it SOLO are welcome too ! - Job Offerings - Unreal Engine Forums!
read it carefully please.
Why we do 2 games in same time? Because they are totaly différent to build, for exemple the swords arena project have tons of animations that are home made and the united zombies use the motion captures packs so less specifics animations to do by hand.
Also we hope to more artists to join us to release one of these project faster.