Running a Guild is tough to begin with (well done Pastoi and the officers) let alone another guild. Thing are much easier with alliances an the alliance chat.
Some thing to consider are:
-different capes. Can be similar, but a guild should have some sense of identity of it's own.
-forum space that is specific to that guild, but other members of the alliance can see and post to.
-The biggest......members. Probably the most important as people will want to join the guild with more players, then be in the little spill over guild.
I'd say take steps to wards requiting members. Possibly starting a new guild, and recruiting people into it under the idea of starting a new Christian guild. To start things off, how about anyone that may have multiple accounts join the new guild with their secondary account characters. That way you have a good base of people that know what is going on in the game, and can check the status of both guilds. Then after a little bit the new guild Will be self sufficient and can stand alone.
just remember....if it's going to be a new guild, then it needs to be a new guild. Would you want to be in a guild that was just the overflow of a larger one? doesn't quit sit well you know.