Can virtual machines on different pc's on a network access each other across the network?

The old computers likely depend upon SMBv1 for connecting. SMBv1 has been removed because it is a gaping security hole.

Truly, best to replace the software with newer software that works in a modern environment.

Can virtual machines on different pc's on a network access each other across the network?

Yes, if set up correctly. Remember that virtualizing is done a lot with servers.

I setup a lab on a couple of Win10 computers with Hyper-V Win7 clients and they don't see each other.

How exactly did you set them up? Could be something involving firewall software or Windows Firewall. Things such as network discovery and the like may need to be turned on.

But clearly, the most idea solution is to modernize.

The computers do not connect or have access to the internet so I'm not looking at this as a security issue.

Your host computer has to (likely) enable SMBv1 and will have to update from time to time, so security does remain an issue.

I'm not sure why SMB1 ever came into this discussion, so let's go back to your question.  I don't have much experience with HyperV, but I use have been using VMware since v1, so I'll use the terms from that product line instead.

When virtualizing, you have several options to deal with the networking.  In its simplest form, you can configure Bridging mode for the network connection -- this makes the VM look just like a distinct computer directly on the network.  It gets its own IP address in the normal IP address range, and it communicates normally -- and the hypervisor passes all traffic through the NIC.  If you set it up this way, then each machine should be able to see each other.  You can check this by doing an IPCONFIG on the host workstations, noting the network addresses, then doing the same in the VM's.  If you are bridging, then you'll likely see all the same subnet -- such as 192.168.1.x.

Another option is to use NAT addressing, where the host sets up a local, private IP segment, and VM's communicate ONLY with the host and with other VM's on the private subnet by default.  This would make communications from a VM on one host to a VM on another host quite difficult -- not always impossible, but EXTREMELY difficult.  If this is your configuration, then your host machine will have an IP address like 192.168.1.x, and your VM will have an address like 192.168.222.x.  Note that each VM may have its own private network, and they may indeed even have the SAME private network -- but open communications won't work through the NAT.

A third option is Host-Only communications -- in this configuration, each VM can ONLY communicate with the local host on a private network.  With this, you won't be able to communicate at all -- it simply won't work.

So -- first verify that you are using bridged networking.  Second, make sure that the machines can PING each other via IP address AND by name.  If not, then you may need to set up a WINS service, set up DNS entries, or set up a HOSTS file (easiest option) on each VM.  For most multi-user systems, PING by NAME is crucial, and without it, nothing else will work. Finally, make sure that any application configuration is done with these names and/or IP addresses in mind.

old computers likely depend upon SMBv1 <-- To be old enough to run out of date software, they are LIKELY to depend on SMBv1

This will be on a closed network with no internet access so that isn't an issue. It sounds from your lively discussion that this doable. I know there are different programs for virtualization so say for Hyper-V do I need more than Hyper-V Manager in Win10 Pro? What would I need to accomplish this with VMware?

You could use Oracle VirtualBox (free), Vmware Workstation ( ~250 USD), Hyper-V included with Windows 10 Pro or higher and almost all server products

Thanks for all of the info. I have marked all comments as helpful. Every post gave me some information.

Moderator, is it possible to close this question as is and split the points?