Im pretty sure LUA can't look at character information in a separate realm folder. The typical structure is WTF>>Account>>AcountName>>Realm>>Character>>Savedv ariables, the saved variables are stored for each character and when a char is loaded in wow the only saved information that char has access to is limited to the realm folder. This means that characters on separate accounts, can not see each others information, this is for obvious security reasons.
Now in game you can send any information you want to another char and any of those chars could store that information for their individual use. This is actually quite simple it just takes a long time for the characters to update each other without spamming themselves offline. Gold isn't too bad, even worn equipment comparison isn't too bad, bank and bag information would be slow. MultiboxerV2 already tries to update each other with bag information each time you open a trade, so loking at that function may help you out. Any addon that remembers an inspected character for you also does the same thing, it just builds a list of items and stores them with a name in the saved variables for the addon.
Anywho, good luck it would be a nice feature to have I just have no where near the time to write and test an addon to do it. Between work and life duties, I have very limited play time and want to get all I can done in that time