"So when it is vested to them on W2 they pay taxes"

Yes, because it's a form of compensation for working there. It's a taxable benefit. Depending on the type of restrictions and the plan, it might be taxable when vested or only when distributed (made available).

"and when they sell the stock they pay taxes again as capital gain?"

The issuing is like the purchase or basis event. There are sometimes fractional sales to cover the extra taxes due at the time of vesting or issuing. Your taxpayer seems to made enough to cover the extra taxes from regular earnings. There might not be a 1099-B; that's a broker form. There might be internal sales, such as an ESOP handles the trades. There will be a statement, then.

Box 14 is an informational box; there is no one standard for its use.