[dossbag]

I doubt that little red wire is a feed to your leisure battery, if you're really intent on taking your leisure battery out then start with disconnecting both positive and negative of the main battery then disconnect evrything from your leisure battery and dont connect anything back up until you put it all back together.
The feed to the leisure battery should be through a substantial sized cable fitted with two hefty fuses, no offence but if you're not sure what you're doing then better find someone who does, you can cause a stack load of damage if you end up shorting something out.

 

[dossbag]

Ok then you need to determine which is your feed to your split charge system and isolated it before you reconnect your main battery, maybe a photo from a wider angle of your main battery and surrounding connections and maybe someone can advise you on what you ned to disconnect and isolate.
Good luck.