Hi,
Reading through the DualDc docs, i would guess that success comes down to your control software on the driving computer. If your software supports all home switches on one input pin.
No two axis can trip the home switch circuit a the same time. Auto homing function of the VSD-E throught firmware doesn't seem to be supported either. Logicaly homing one axis at a time will have to happen on the control software on your PC.
Home connects to Encoder pin 1 on the VSD-E Dual and then to ground. Home signal is passed to VSD-E Dual CMD connector pin 12, but no mention is made of which pin this is routed to on the VSDEPI. Could try loading a port monitor in Linuxcnc and see which pins toggle when you manualy trip the home switchs.
Hope that helps.