[elevensies]

This is a typical short squeeze. ( https://en.wikipedia.org/wiki/Short_squeeze ) [ With the caveat that I'm far from an expert on this, I just have a collection of documents of many failed corners and very few successful corners. ]

The short sellers are anyone with a negative outlook on the stock. For example, some hedge funds do 50% buying, 50% short selling, so in theory they are neutral to overall market conditions.

The brokers in this case have been permitted to lend out the stock to earn extra money, the short sellers are ordinary customers of the brokers, the short sellers don't necessarily have any special relationship with the brokers.

The market maker would be buying as much as selling, and not holding any position over extended time, so they don't influence this event.

In theory, the short sellers have to pay up to meet their obligations.