It's a good question, and Tolkien didn't really touch on it.
With the Feanorians, we know that some helped kill men, women, and children. But some stood aside or abandoned the Sons of Feanor (at both Nargothrond and the Third Kinslaying), and some died defending the Havens. But we don't know what the more violent ones were thinking and feeling. I'd like some to stand aside at the Second Kinslaying, though in smaller numbers.
Personally, I'm OK with there being more than just 5 Elves who do evil things without much remorse, although there shouldn't be tons of them. I think in "Quendi and Eldar" there's a comment that some Avari were pretty bad people, though none were as bad as Eol.
We have a few options with Eol's friends:
1. They help Eol do wicked things. They may or may not feel conflicted.
2. They're unaware he raped Aredhel (to whatever extent we make it a rape) but otherwise help him do bad things. May be conflicted.
3. They start to feel like he's going too far. When Aredhel and Maeglin leave, Eol's friends purposely don't intervene. They do tell him his family left, but he can see that for himself.
4. They start to desert him before Aredhel and Maeglin do. Maybe even before he meets them. Losing his buddies drives him more over the edge into control-freak mode who won't let ANYONE escape him. This would be interesting, but I don't know that it's worth it to take the time to show his buddies deserting him, unless they do so during episodes that already deal with Aredhel.
5. Get rid of them. Not my favored approach, personally.
In any case, I imagine he only has 3-4 followers.