The UWP Task Manager is not very reliable when it comes to killing Win32 applications I have found. It is not only VMware Workstation that it can't kill.
You could try Process Explorer from www.sysinternals.com (redirects to the correct Microsof TechNet URL that I can never remember) Which is a Win32 application so should have no trouble killing the rogue Workstation instances.
Also so worth a check in Windows Security Center that there are no hardware security features or Virtualisation Based Security features enable that might disrupt Workstation. (All my processors are too old for these features so I can't give any first hand pointers to what might be there.)