Well we don't know what consciousness is yet but I think if the human brain can handle one "consciousness" it can handle multiple partial ones, especially when in dreams where your brain can run much more efficient. But as I said we need to know what consciousness is before we can answer this question

I also think multiple personality disorders prove that human brain can simulate multiple people

Some characters don't panic and calmly ask questions like "Will I die if you wake up", "Is my whole life a lie, am I just an actor to you". It geniunely makes you feel bad for simulated characters inside your brain. That's why I don't do that much

Have you ever tried to render and touch a highly complex mathematical/abstract object like the Mandelbrot set?

Imma try that next time but it will prob just crash or look blurry. But the brain doesn't work with maths, it's more similar to an image generation AI