Oh, trust me, while I may not be able to sympathize with everyone, I and empathize with a TON of people. Empathy seems to be my specialty.
Anyways...
The thing is, you as the writer know EXACTLY what these secondaries are thinking. So writing them as if you don't is impossible. And can also lead to a horrible case of talking to yourself when your characters need to interact when you're not careful. But that's the thing. I think of any character (given emphasis via CS) being controlled not as primaries or secondaries, but as a main character. The idea of primary and secondary was only introduced to me after you made mention of the third person narrative. Normally, I would try to give them equal time, but here I can't. Aya's my main, Leon is my secondary. Which brings up another point. What are the secondaries gonna do when the mains are gone? If they are used as you like, it's no biggie. They can vanish and it's not important at all. Only if a main is nearby will they even be mentioned. We have no clue what Sebastian is doing or where he is unless it's mentioned in a previous or future post. Until a main talks to him, he's completely irrelevant. But when you treat them like I like, you have a problem. There is always something they can do, but it has to be detailed. Plus they now have the job of handling any third person characters. Like in a novel, how there may be three main characters. The third person ones interact with them and that's all we see of them. Ever. But if the narration switches to characters besides those three. You get a temporary main. Someone who takes over the role of first person so the third person characters can have someone to interact with. I don't know, it just doesn't seem like a good idea to have a third person as one of your personal characters, but what the hell do I know? This is the first time it's ever come up in my 5-6 years of RPing.
And by the way, if it seems like this was weird, I was literally writing my points as they came to me.