You can always find a plausible reason to get rid of an employee (Meaning one that will keep you out of a wrongful termination lawsuit). If nothing else, there is always "Re-alignment of priorities" or "Consolidation of responsibilities" or just plain downsizing. I've seen it done dozens of times in the company I work for. Savvy managers know how to do it right so the company stays out of legal trouble. Those same managers know how to keep their own jobs secure.
Why would they lay off three other employees at the same time?