Yes, and yes. The sibling comment here about liquidation preferences is correct, and these separate incentives are usually structured as retention incentives — eg, compensation for future work with the acquiring company.

Shareholders are of course free to sue the board for acting outside of the interests of the shareholders overall, but this happens very rarely because typically the company would otherwise be shutting down and it’s very hard to make the argument that the deal undervalues common shareholders’ shares.

Because “shares” are not all the same. Preferred vs common, so unless you negotiated some kind of preferred share terms, assume your shares are worthless. For a non publicly listed company. For a publicly listed company, the details are all publicly available, so the different types of shares will have their different prices be easily available to see.