Here's an example of a location where the inhabitants are supposed to all be the same faction, but kill one another as soon as you enter the cell.
Upon entering Odirniran [CELL:014802C8] (as a member of House Hlaalu for the Telvanni at Odirniran quest), Haleneri Salor [ACHR:01813E5C/NPC_:0126016F] and Valyne Vedaren [ACHR:01813E5B/NPC_:0126016E] immediately attack Remasa Othril [ACHR:01813E5A/NPC_:0126016C].
I used the "stopcombat" command on all 3, but then they immediately turned to attack me (I'm supposed to talk to Remasa Othril for the quest). I used "stop combat" and "moddisposition 14 100" to make them stop attacking me, and then they went back to attacking one another (eye-roll emoji). I finally resorted to a script to stop all the shenanigans (see below).

After rescuing Vedelea Othril
After rescuing Vedelea Othril [ACHR:0181B890/NPC_:01260170] from OdirniranVSTower "Odirniran, Tower" [CELL:014802C9] and leading her back to her sister, she is immediately attacked by Haleneri Salor [ACHR:01813E5C/NPC_:0126016F]. So I extended my script:
; Remasa Othril [ACHR:01813E5A/NPC_:0126016C]
"01813E5A".stopcombat
"01813E5A".setav 33 10 ; Aggression
"01813E5A".moddisposition player 100
"01813E5A".moddisposition 01813E5C 100
"01813E5A".moddisposition 01813E5B 100
"01813E5A".moddisposition 0181B890 100
; Haleneri Salor [ACHR:01813E5C/NPC_:0126016F]
"01813E5C".stopcombat
"01813E5C".setav 33 10 ; Aggression
"01813E5C".moddisposition player 100
"01813E5C".moddisposition 01813E5A 100
"01813E5C".moddisposition 01813E5B 100
"01813E5C".moddisposition 0181B890 100
; Valyne Vedaren [ACHR:01813E5B/NPC_:0126016E]
"01813E5B".stopcombat
"01813E5B".setav 33 10 ; Aggression
"01813E5B".moddisposition player 100
"01813E5B".moddisposition 01813E5C 100
"01813E5B".moddisposition 01813E5A 100
"01813E5B".moddisposition 0181B890 100
; Vedelea Othril [ACHR:0181B890/NPC_:01260170]
"0181B890".stopcombat
"0181B890".setav 33 10 ; Aggression
"0181B890".moddisposition player 100
"0181B890".moddisposition 01813E5A 100
"0181B890".moddisposition 01813E5B 100
"0181B890".moddisposition 01813E5C 100