There are four of them:
a choice of a warrior or a Druid (Marcus, Rhian) for a Roman party and
a choice of two warriors (Brigid, Numerius) for a Celtic party.
If they join the party they are always found in the #5 slot, they can never switch places with other party members. This is just wonderful for the Druid. For the other three NPCs, the warriors, it means usually having them at the wrong end of the party.
Unlike the PCs, their stats are not generated with skill points, said stats are a function of each NPC's level. That is why the stats are following such unusual patterns.
NPCs are slightly modified versions of mainstream creatures:
Brigid is just a Britannian Warrior
Rhian is an Elder Druid
Numerius is a Roman Soldier
Marcus is a Centurion
It seems to be possible to modify them, I am working on that now. Alterations only require simple alterations to Corescendata.txt.
A spellcasting Brigid:
The list of the stats:
Stats are altered the same way as in BoA, with the calls, which_to_add_to[#] specifies which stat is to be modified, how_much[#] specifies the amount of the increase, # is from 0 to 5.