Do the Win7 PCs see each other?
The Win7 PCs not seeing the Win10 PC may be due to Microsoft also disabling (i.e. set to Manual start) two critical Services in Win10. You need to make sure that the following two services are running:
Function Discovery Provider Host
The FDPHOST service hosts the Function Discovery (FD) network discovery providers. These FD providers supply network discovery services for the Simple Services Discovery Protocol (SSDP) and Web Services – Discovery (WS-D) protocol. Stopping or disabling the FDPHOST service will disable network discovery for these protocols when using FD. When this service is unavailable, network services using FD and relying on these discovery protocols will be unable to find network devices or resources.
Function Discovery Resource Publication
Publishes this computer and resources attached to this computer so they can be discovered over the network. If this service is stopped, network resources will no longer be published and they will not be discovered by other computers on the network.