There's a couple of different things going on here. The latter part of your question, the laptop-to-PC issue, is likely as you suspect — because the laptop is on a separate LAN from the desktops (each router being its own local network), neither side can browse for computers on the other. You very likely could access the wired PCs from your laptop, if you connected to them directly by IP address. (Say, by entering
\\192.168.12.34\ into the Windows Explorer address bar, if that was the IP assigned to one of your desktops.) It's merely the browsing and discovery functions which don't work, since they're confined to the immediate LAN.
Not being able to browse for the files on your Android phone, though, is an entirely different issue: You can't remotely access the files on an Android phone, because Android phones don't do Windows file sharing — at least not by default. Most likely, with your stock phone as configured by the manufacturer, the only way to remotely access its files is over Bluetooth from a paired computer.
ES File Explorer knows how to speak Windows file sharing as a client, so it's able to connect to the files shared on your PCs. But to go the other direction, you need to install an app on your phone that'll act as a Windows file sharing server. I'm sure there are several choices available in Google Play. (However, you should think twice or more before doing something like that. Opening up remote network access to your phone's files carries serious hacking and privacy dangers. It's not something to undertake casually.)