I'm not a guru at all when it comes to the emu , as I'm still new and learning.
However here's what I'm getting from your posted problem.
A+C are fine when they're running both the server , and client together. Only a problem when B or D try to log in.
eqgame.exe and associated binaries are the same on all machines? I'm taking this as a yes.
What mini-login version are you running? ( Mini-login version 6.2 is compatible with the 0.6.4 database.
Since the problem comes from an error only when logging on from a different computer , perhaps a router / firewall problem ?
I remember seeing posts about 1017 errors , and fixes all through the forums.
Perhaps one of these may help you.
NAT Fix
Error 1017
( Edit : Try doing server / client on B + D and see if it works , if it does then it's gotta be something between your machines thats keeping them from connecting properly. just my 2cp. )