Windows Server may have CALs included if you buy a retail (box) or OEM (preinstalled) product, but volume-licensed editions have no CALs included. In the first case, different numbers of CALS are available for different prices, and these bundles are differentiated by part number.
You can use CALs in two licensing modes with respect to Windows Server.
- Per-server: Each server has a number of CALs assigned to it, and so if client machine A connects to three servers that are each in per-server mode, that machine will use three CALs.
- Per-device or per-user: Each device or user has a single CAL assigned to it, and it can connect to any number of Windows Server instances using that one CAL. With per-user licensing, 25 User CALs will allow 25 users to connect to any number of server machines from any number of client machines. With per-device licensing, 25 Device CALs will allow any number of users to connect to any number of servers from 25 devices.
You can mix per-device and per-user CALs in your organization to save money in some cases, but it is probably more trouble than it is worth. I have never found a reason to use per-server licensing in an organization with more than one Windows Server. I'm not sure if FPP and OEM bundled CALs are per-user or per-device, or if you get to choose.
To answer your specific questions:
The 25 CALs apply to all of your physical and virtual machines if you use them in per-user or per-device mode, but you would need 100 licenses if you operated each virtual machine in per-server mode. (If the host was running Windows Server roles that clients connected to as well, then you would need a total of 125 CALs in per-server mode, but it sounds like you are using it solely as a VM host.)