For the party editor, you need to copy the necessary scripts out of the SoZ campaign folder. There are a good number of other scripts in there that are just handy to have around, too, like gc_npc_tag, which allows you to create special dialogue for any companions you may design, so you might want to just copy all scripts from the folder.
The way you'll want to do a party loop is like this:
object oPartyMember = GetFirstFactionMember(oPC, FALSE);
while(GetIsObjectValid(oPartyMember))
{
//do stuff here
oPartyMember = GetNextFactionMember(oPC, FALSE);
}
The two "FALSE"s are necessary for it to consider your party members as valid PCs.
Also, I recommend opening up the Storm of Zehir campaign and checking out the party registry book so you can see what scripts they're calling and how they handle party management.