To clarify a few points here:
Running two brushless motors from the same esc: you can't, it will not work. They might start and run together, but they won't work right for long. As soon as one slows down, the other may well get out of sync, lose power, run backwards, etc. Not good. If it worked for a short time, they would run at exactly the same speed though.
As regards the ESC and motor working together, it's something like this:
The ESC senses the motor position, and gives the output accordingly. There isn't any one set speed, the ESC just applies power using the motor's position to know which windings to activate. It's like an old clock with a pendulum: the clock senses the position, and adds a little power to make it go more in that direction. Starting is somewhat different, but that's another topic
So it's not that the esc "reduces speed if the motor falls behind", more like "the esc always knows where the motor is, and powers accordingly".