I see you need some help with multi disc games. Heres an extract from the readme file. Note 9: Multigame discs can be created with "GCOS MultiGame Creator V4F.exe". Note 12: When you have both discs of a game burned within one multigame ISO image, you can switch the disc by ejecting and reinserting the disc. But you need first to select the second disc with button Z on the startup screen (green GC logo). Note 22: If the second disc is not a multi game disc you need to change to first entry [0] and press Z, so it can be detected after disc switch. Note 25: The loader will save the offset of the second disc (pressing Z) also, if you change the disc. So you can use 2 disc games where the games are on different multi game discs.
Heres guide for multi game gc discs. [WII] How to create a disc containing multiple gamecube games
