It's kind of implied in the game that Eddie and Volt are connected (beyond Eddie creating Volt). Like when Volt blacked out, Eddie felt it too.
So that leads me to headcannon that as well as sharing pain, they also share pleasure. They don't share all sensations. Like, Eddie can't feel when Volt picks up a glass. But when a sensation is particularly strong, be it pain or pleasure, it's shared.
They're probably aware of the pain aspect, but I don't think they know about the pleasure aspect. When the two fucked before meeting the player character they just assumed any pleasure they felt was their own.
Now imagine the player character coming along and fucking one of them, and the other, for reasons unknown to them, start feeling pleasure...
Imagine pulling Eddie into the backroom during a show and fucking him against the desk, and Volt feeling the pleasure like it was his own. His face flushes as he looks around, wondering what could be the cause, and his eyes land on the backroom. He just Knows what's going on in there.
But he has to entertain, especially as Eddie and you are currently busy. So he has to try and push his arousal down.
Then later on, after Volt talks about the sudden pleasure he felt, tying Eddie to the bedframe and fucking Volt while Eddie watches. Not touching him until he gives in and begs to be touched.... edging both of them even though you're just touching Volt...