Alayne

No need to change the the register_aid saving or the point giving. 
You're just currently giving the points to the wrong person. Right now, you're checking the logout / die event, so you're on "losing char", and give points to him. You need to attach the script to the remaining char before completing the final stage.
Add this line:
attachrid(.register_aid[0]); After this one
killmonsterall "guild_vs5";  

.char_id[getarraysize(.char_id)] = getcharid(0); You can't use .@char_id, as @ means temporary bound to the npc variable. It'll be cleaned when the script will hit it's end, and won't be shared through two instances running the script.
On the other hand, with this method, you'll have to handle the cleaning manually.

Ok peoples, here you are. I used item_info_re table in database, but you can change it to item_info according to your own setup.
Also, I just list scripts on items + cards coumpound. If you need the set to be added, you'll have to add it ^^
resistantInfos.txt

Change this line on OnReadyCheck label :
else if( .@Guillaume < 10 || .@Croix < 10 ) Change the '10' for the selected amount of player.

There. I've added a code portion to prevent "all items sell", and moved the array of sold items filling so items which doesn't give point won't be deleted.
costumetrader.txt

Allright peoples I've finally fixed everything.
There was several issue, one with the getpartymember, which was called with bad id and therefor wasn't filling the temp array properly (that's why I was warping players from second team, not first one)
And another was with the "talking" variable, which, as megu (I think) said, was shared between instances and therefor block the second team going.
Thanks anyway peoples!

Finally, as expected with the last comment, it was a matter of level error, while no error is raised. The mobs just don't pop the skill if it doesn't match the highest level cap.
Problem solved.
 
Well actually I found yesterday evening what's happening with the areamobuseskill ones.
It's due to the lvl I used. Storm Gust is limited to lvl 5, while I wanted it to be buffed, and poped a lvl 10.
While it didn't worked, it didn't poped an error message either...It made me lose a bunch of time, but now it's working well.