Graal copyright / ownership

How far do the rights of Graal reach regarding ownership / copyright protection?

Are old server files owned by graal? Or are they the property of the original authors? Or public domain?

Is there any way for what “Graal Reborn” aimed to do could be set up so that it is no longer an infringement of any copyright?

They have rights to the name and the domains. I doubt anything else has been actually legally protected. Making a game similar to Graal is not an infringement of any copyright protection.