Solution #1.
Install Virtualbox on the Windows machines, then create an Ubuntu virtual machine on each of them.
or the better alternative
Solution #2.
The Cool Way, accessible from any Browser and Device without any RDP Client
Install Ubuntu on a powerful computer(server), with at least 6 GB RAM.
Install the Ubuntu MATE desktop and XRDP.
On that Ubuntu computer you can create the 25 users (not root users) above mentioned.
Setup Apache Guacamole on it.
In the user-mapping.xml file you need to add the 25 allowed users and connections.
Here is an example with 5 users = 5desktops + 1 ssh:
<user-mapping>
<authorize
username="demologin"
password="demologin1234">
<connection name="SSH">
<protocol>ssh</protocol>
<param name="hostname">localhost</param>
<param name="port">22</param>
<param name="username">student1</param>
</connection>
<connection name="student1-rdp">
<protocol>rdp</protocol>
<param name="hostname">localhost</param>
<param name="port">3389</param>
</connection>
<connection name="student2-rdp">
<protocol>rdp</protocol>
<param name="hostname">localhost</param>
<param name="port">3389</param>
</connection>
<connection name="student3-rdp">
<protocol>rdp</protocol>
<param name="hostname">localhost</param>
<param name="port">3389</param>
</connection>
<connection name="student4-rdp">
<protocol>rdp</protocol>
<param name="hostname">localhost</param>
<param name="port">3389</param>
</connection>
<connection name="student5-rdp">
<protocol>rdp</protocol>
<param name="hostname">localhost</param>
<param name="port">3389</param>
</connection>
</authorize>
</user-mapping>
This all can be done on a single Linux computer.
Guacamole supports multiple connections, copy and paste, audio etc.
Taking screenshots is also very easy, as there is an Application installed with Ubuntu MATE.
The Full Tutorial how to do it and the DEMO is can be found here: https://vpsghost.com
In the Demo I have setup the five users with the user-mapping.xml above:
The first login:
Username: demologin
Password: demologin1234
XRDP Login
Username: student1
Password: student1
Username: student2
Password: student2
and so on...