Not being a MAC forum, I'm not sure how much help we can be, I can suggest some options for your Win7 machine(s) first off
Check and make sure these Services are Started on the Win 7 machine(s)
Workstation
DHCP Client
DNS Client
Server
TCP/IP Netbios helper
Computer Browser
Make sure Network Discovery is turned on, on the Win 7 machines
Make sure file and printer sharing is enable on both and that local firewalls are supporting it. Temporarily uninstall any third party firewalls or Internet Security Suites that may include some type of Firewall applet.
Make sure NetBios over TCP/IP is enabled in the properties of IPv4 on you network adapter. And uncheck IPv6 for now.
Look for Bonjour service and temporarily set it to manual or disable and stop, same with mdnsresponder. Also check services near the top for a peculiar string containing numbers and or special characters, disable and stop
Also on the Win 7 machine(s) open the Network and Sharing Center and choose Change Advanced Setting and make sure it looks something like this (see attachment)