Hi As the NPC level up are quite buggy, I'd like to hack a little bit those I have in my party. Especially increasing Meleny's wisdom so she can have Lv5 spells, and fixing Elmo's dual wield. In which files can I find their current informations ?
You'll have to edit the protos.tab file. Also note that while incresing stats scores doesn't mean you increase spell use. Spells are listed at the end of the row of the NPC you are editing. IOW, you must hand pick and type what spells an NPC has access to and you get a limit of 20 total (for all levels).
There is a file in tooe3.dat called levelup.tab. It has what I think are the end results of the level-up schemes for all the npc's in the game. I haven't done any experimenting with this file, but you might be able to make something happen with some trial and error. But if I had to guess I'd say that any changes you make in this file would, at best, only work for a new game. I'm not sure if you can hex-edit Npc's or not. I know someone on the Atari board has developed a character editor, but IIRC it only covers a few things (stats, gold, exp) and only works for pc's. You might try sending a pm to the guy who made that program. I think his name is Ferros. Search on the atari board for "hex editing."