1st of all the source code is from skacikpl's then i modified it to spawn 3 companions.
Source Code: http://www.nexusmods.com/witcher3/mods/348/? 
and just like what skacikpl said there's 50% chance that you haven't set-up your mod scripts properly and 49.99% chance that you have mod conflict. Remainder 0.01% chance is actually issues caused by the mod itself.

""""""""""""""""""""""""""and if you have script compilation error don't be shy to tell me the problem and i will try to fix it. but you can try downloading this 1st before telling me http://www.nexusmods.com/witcher3/mods/897/ then search for file called "Vanilla CDPR script v1.22" then extract it to GOG games\The Witcher 3 Wild Hunt\content\content0, replace if needed"""""""""""""""""""""""""""""""""""""

IF you get an error like this: 

Error [content0]game\behavior_tree\tasks\monsters\bttaskmaintainspeed.ws(10): Class 'CBTTaskMaintainSpeed' already defined.
Error [content0]game\behavior_tree\tasks\monsters\bttaskmaintainspeed.ws(74): Class 'CBTTaskMaintainSpeedDef' already defined.
Error [content0]game\behavior_tree\tasks\reactions\bttaskisman.ws(4): Class 'CBTCondIsMan' already defined.
Error [content0]game\behavior_tree\tasks\reactions\bttaskisman.ws(15): Class 'CBTCondIsManDef' already defined.

then kindly go to GOG games\The Witcher 3 Wild Hunt\content\content0\scripts\game\behavior_tree\tasks\monsters\ and delete bttaskmaintainspeed, 
and go to GOG games\The Witcher 3 Wild Hunt\content\content0\scripts\game\behavior_tree\tasks\ and delete bttaskisman.ws.

using trainers such as FLING 3DMGAME might break the mod causing one of the spawned companion run like and pusing the enemy when engaging a battle

CHANGELOG:
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UPDATE 2.1:
FIXED IMMORTALITY BUG(THIS IS A CODING MISTAKE FROM THE ORIGINAL SOURCE CODE AUTHOR AND I'VE ONLY NOTICED ITS FLAWS RECENTLY. SORRY)
UPDATE 2:
Added 2 files for NG+ savegame and NON NG+ savegame
Fixed bug that sometimes a companion hud will show up even if not enabled.
Fixed bugs for Companion #2(sometimes it doesn't attack)
Fixed Regis and Dettlaff now they fight with super powers.
Companions can now use TORCHLIGHTS(see below how to use)
Added prefixed spawn commands. ex. typing WolfTeam instantly spawns vesemir, lambert, eskel
Added more npcs.

prefixed spawning codes: 

ex. TeamName(want immortal, want tag)

WolfTeam(1,1) --// Vesemir, Eskel, Lambert
FamilyTeam(1,1) --// Ciri, Yennefer
CatTeam(1,1) --// Gaetan, Keyan(demonwitcher), Tauler
AllSorceress(1,1) --// Yennefer, Triss, Keira
VampireTeam(1,1) --// Coroner Vampire, Regis, Dettlaff
BlinkTeam(1,1) --// Ciri, Olgierd, Regis
AllRounderTeam(1,1) --// 1 bowman(scoiatel), 1 mage, 1 tank(shield + sword)

you can still make your own team by editing the function ST() at spawncompanions.ws

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UPDATE 1: 
Shortened Commands
ex: 
SpawnCompanion(Triss,1,1,1) is now SC1(Triss,1,1,1)
RemoveCompanion(Triss,1,1,1) is now RC1(Triss,1,1,1)
CallCompanion(Triss,1,1,1) is now CC1(Triss,1,1,1)
SneakyLikeRoach is now CB1
TagCompanion is now TC1
SpawnTeam is now ST
CallTeam is now CT
RemoveAll is now RA

Fixed bugs that when spawning some npcs in 1st companion it doesn't attack
Added more NPCs to spawn
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LIST OF NPCs you can spawn: CASE SENSITIVE CODES
NAME-----------------------------------SPAWN-CODE
//normal game
update 1:
Cirilla----------------------------------Ciri, Cirilla
Lambert-------------------------------Lambert, lambert
Vesemir--------------------------------Vesemir, vesemir
Eskel-----------------------------------Eskel, eskel
Letho----------------------------------Witcher, witcher
Dijkstra--------------------------------Dijkstra, dijkstra
Dandelion------------------------------Dandelion, dandelion
Zoltan----------------------------------Zoltan, zoltan
Emhyr----------------------------------Emhyr, emhyr
Hjalmar--------------------------------Hjalmar, hjalmar
Vernon Roche--------------------------Vernon, vernon
Voorhis---------------------------------Voorhis, voorhis
Nathanel-------------------------------Nathanel, nathanel
Menge----------------------------------Menge, menge
Udalryk---------------------------------Udalryk, udalryk
Von--------------------------------------Von, von
King of Beggars------------------------KingBeggar, kingbeggar
Margarita------------------------------Margaritta, margaritta
Rosa------------------------------------Rosa, rosa
Fringilla-------------------------------Fringilla, fringilla
Avallac'h-------------------------------Avallach, avallach
Baron----------------------------------Baron, baron
Crach----------------------------------Crach, crach
Coroner Vampire---------------------CoronerV, coronerv
Eilhart---------------------------------Eilhart, eilhart
Keira-----------------------------------Keira
Yennefer-------------------------------sorceress (NOTE: typing yennefer instead of sorceress spawns a normal NPC that doesn't attack and gets scared of fights)
Triss------------------------------------Triss, triss
Kiyan(Demon Witcher)---------------DemonWitcher, demonwitcher
update 2:
Cerys---------------------------------Cerys, cerys(NOTE: NPC only)
Ermion-------------------------------Mousesack, mousesack
Thaler--------------------------------Thaler, thaler
Gaetan-------------------------------Gaetan, gaetan(NOTE: bug - he doesn't use his sword)
Tauler--------------------------------Tauler, tauler
Scoiatel Bowman--------------------ScoBowman, scobowman
Knight with Shield and sword------EliteShield, eliteshield
Ves------------------------------------Ves, ves

//blood and wine
Syanna--------------------------------Syanna, syanna (NOTE: Spawning her spawns random template of her(naked, hooded, normal), you might wanna spawn her multiple times before getting the template you want)
Anna---------------------------------Anna, anna (NOTE: just a normal NPC, she does not attack)
Dettlaff-----------------------------Dettlaff, dettlaff
Regis--------------------------------Regis, regis
Milton-------------------------------Milton, milton
Palmerin----------------------------Palmerin, palmerin
Guillaume--------------------------Guillaume, guillaume
update 2 
Gregoire----------------------------Gregoire, gregoire

//hearts of stone
Shani-------------------------------Shani, shani (NOTE: just a normal NPC, she does not attack)
Olgierd-----------------------------Olgierd, olgierd (NOTE: sometimes when he is spawned and attack an enemy it doesn't hit like 100% miss attack respawn and respawn him until he can hit enemies normal, HE IS MY FAVORITE COMPANION)
Iris----------------------------------Iris, iris (NOTE: just a normal NPC, she does not attack)
Horst-------------------------------Horst, horst
Ewald-------------------------------Ewald, ewald
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///////////////////////CONSOLE DEBUG ENABLER IS STRICTLY NEEDED BEFORE INSTALLING THIS MOD////////////////////////////////////////
INSTALLATION: Extract modSpawnCompanions.rar to GOG games\The Witcher 3 Wild Hunt\Mods(create folder if you dont have)
Then go to MyDocuments\Witcher 3 and open or create Mods.settings file (make sure it's not Mods.settings.txt!) and add following lines:

[modSpawnCompanions]
Enabled=1
Priority=1

Usage:
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Spawning a companion:

NOTE: YOU CAN ONLY HAVE 1 COMPANION TO HAVE A HUD

Ex: SC1(NAME, SHOWHEALTH(OPTIONAL), SETIMMORTAL(OPTIONAL), NAMETAG(OPTIONAL)
1 = true, 0 = false 
sample codes:

SC1(Triss, 1, 1, 1)
SC2(Ves, 0, 0, 1)
SC3(Ciri, 1, 0, 1)

If you want to spawn 3 companions immediately you can type "ST" in the console but the default would be Olgierd, Ciri and Avallach if you want to change the 3 immediate companion spawn. Open SpawnCompnaions.ws from modSpawnCompanions\content\scripts\game then CTRL + F find "exec function ST()" you will find the code:

exec function ST()
{
SpawnCompanionQuick1('Olgierd', 0, 1, 0);
SpawnCompanionQuick2('Ciri', 0, 1, 0);
SpawnCompanionQuick3('Avallach', 0, 1, 0);
}

then change the values inside SpawnCompanionQuick()
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Removing a companion:

RA --//immediately removes all spawned companion
RC1 --//remove companion1
RC2 --//remove companion2
RC3 --//remove companion3
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Teleport companion next to player:

CT --//teleports all companion spawned near you
CC1 --//teleport companion1
CC2 --//teleport companion2
CC3 --//teleport companion3
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Teleport companion behind camera:

CB1 --//Call companion1 behind camera
CB2 --//Call companion2 behind camera
CB3 --//Call companion3 behind camera
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Tag Companion (Puts Companion # above them):

TC1 --//Tag Companion1
TC2 --//Tag Companion2
TC3 --//Tag Companion3
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Companion Torchlight (gives companion a torchlight:
IMPORTANT NOTE: SOME COMPANIONS WON't BE ABLE TO HOLD THE TORCHLIGHT CORRECTLY ex: Ciri is holding the torch sideways
CET1 --//Give Torchlight to Companion1
CET2 --//Give Torchlight to Companion2
CET3 --//Give Torchlight to Companion3

CLT1 --//Light upTorchlight on Companion1
CLT2 --//Light upTorchlight on Companion2
CLT3 --//Light upTorchlight on Companion3
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