I don't know if you've tried this...to work w/
....You've mentioned this is a router, but does it function as a switch as well? (many devices can function in either mode)
If it does I would set all machines to the same range of IP addresses *192.168.0.xxx /24* for example. This may allow the machine to just act as a switch and solve the problem for you...
... If nothing else it's just something else to try... Hope you get it fixed.