Jesus, name and shame. That kind of behavior should follow those founders like a sign hanging from their neck saying "don't work for me."
That would be a fairly straightforward lawsuit as a company cannot intentionally defraud its own shareholders.
If the employees had options they weren’t shareholders (yet)
That's a straw man argument. If you had an interest of any kind in a company, and someone screwed you, you can sue. In today's environment, companies will settle even if they have a good case, let alone if they are likely to lose. Plenty of lawyers will take such a case and get paid in a contingent fee arrangement.
The company was sold to a large tech company for like 350mil but what happened first is the VCs/founders created a new company and sold the IP from old company to new company and sold the new company for the 350mil leaving the employees with a worthless company.
So also trusting the founders and the VCs they choose are in my opinion more important then any equity grant offer