I have somewhat of an issue, not sure if anyone knows how to solve it.

As followers I have Illia and Vigilance.
Sometimes when Illia casts a massive frost spell Vigilance gets caught up in it and starts attacking Illia.

There seems to be something wrong with the settings in the game that allows follower on follower hostility if attacked.

Does anyone know how to solve this?

Get a follower that does not cast magic. Or, does a better job of aiming.

Friendly Fire is an issue with followers in this game.

Yeah thanks...

Not quite the answer I was looking for or hoping to get...
I was actually hoping that someone would know how to fix this, maybe with a console command or a mod that would solve it.
I did look around for mods but none seem to work, either on the Nexus or the Steam Workshop.

I had this problem with a mage follower and Shadowmere. They would always end up fighting each other, and I would have to reload a previous save. I dropped the follower and kept Shadowmere.

Sorry that the news what not what you wanted. However, to stop a follower from attacking another follower because they were attacked by that follower would mean that they would not attack anyone who attacks them.

So, the advice I gave you is appropriate, with the conditions of the game. You can use a console command to stop combat on a follower, but that stops all combat for that follower. But, I did not think that was what you wanted.

Unfortunately at the moment that is the only answer. Friendly fire is on by default; therefore followers will friendly fire each other (and/or you, and/or you'll friendly fire them), which can cause hostility in some instances.

There's currently no mods for this, presumably because friendly fire is a global thing in-game and disabling altogether would have some unforeseen consequences elsewhere. Give it time. The Skyrim modding community (post-CK release) is still fairly young; someone may be able to come up with something eventually, but it will take time. Even then some things are never quite fixed...derp AI being one example. Years later, NPCs in Oblivion still act like they've recently recovered from lobotomies.

For now, you can try the "resetAI" console command but I'm not 100% sure this will work as intended. Never used it myself; it may break other AI routines for that follower. Otherwise, I'd recommend either leaving Vigilance behind in combat or, if you must have multiple followers, finding one who is less of a "nuke it from orbit" type.

I guess so...
I was actually hoping that hostility detection would go through the player relationship settings with the target that is inside the detection range and then allow the followers to determine what NPC is a valid target and what isn't, not just on attacking whatever has damaged them that isn't the player or scenery.
What I mean is, if the player relationship with the target is hostile, the followers would see the target as hostile as well, however if the relationship with the player is neutral or friendly the followers would not attack that NPC.

I guess this could however cause problems with the brawling quests, since the followers won't attack the NPC that the player is having a fistfight with, and the NPC is set as hostile to the player during the fight.

But well... I guess this would require a huge amount of programming.
And I'm not a programmer and have next to no knowledge of how to work the Creation Kit. So I just wait and hope someone else will solve it. Hopefully, some day...

how do you get 2 followers? i thought you could only have 1 at a time.. i guess i'm wrong. I have marcurio currently, who else can or should i get?

I once had a follower who always killed innocent animals. So one day i got sick of it and wasted his sorry ass!

Vigilance is the dog you can buy in Markarth. You can have him along with you as an additional follower

oh ok makes sense now, ty

Not quite two followers, but there are some dungeons where one or two others tag along in addition to a follower. Having a group is a pain because of narrow passages, especially when the follower is a mage. I usually have my follower wait until the dungeon is cleared.

Having more than one follower is a total pain in the butt, including dogs. Having a horse and a follower in combat is a total pain in the butt. I never choose to have more than one personal follower at a time, I got a mod to make horses run from combat instead of being stupid, and I cringe whenever I have to suffer through a quest that forces a secondary follower on me, and just try to get through them as quick as possible. If the quest follower was too big of an annoying PITA while I was forced to work with them, then I take great pleasure in cutting their throats after it's done. I don't suffer digital fools well. And that's how I play the follower game.

for comparisons-sake and to show that gamesas has implemented a follower system that worked: fallout3.

there was a special thread on the forum that showed how to gath ALL the companions and adventure in the world without hardly any bugs, at all.

you could get all the companions to work as a team and it was a blast.

There is a "Friendly Fire" mod on Steam Workshop that stops followers from attacking each other if there are stray casts.

Also the latest version of UFO prevents followers from attacking each other as well.

Friendly fire mod doesn't work, I tried it.
And the UFO mod isn't perfected yet, the modder is still working on it.

Finished a companion quest with the witches then they replaced my follower with a companion, i know i can get him back after but it still annoyed me and i reloaded an old save.