At first, the questions
This PCs are connected to the internet?
This PCs can be reached from the internet - means the Router address is always known or a static IP
The Router allows this direct access (no blocked TCP / UDP ports) WOL uses UDP 7 or 9?
This may help at least for Windows:
https://www.howtogeek.com/192642/how-to-remotely-turn-on-your-pc-over-the-internet/
Also some tools:
https://www.pcwdld.com/free-wake-on-lan-tools
What you should take into account:
A PC that is reachable over the internet is always a nice target for people who like hacking or distribute malware and crapware. At all this PCs should be checked by a professional if someone targeted this systems or tried to access this machines without permission.
Normally WOL is not enough, also RDP is enable (makes a remote desktop connection possible). That can also be security risk. Such a system must be maintained and security fixes must be provided to this systems when available. That affects all operating systems, not only Windows. The problem is only the windows flaws will be communicated on tech websites mostly...