Disable wireless connectivity. Unplug all but one machine. Debug that connection.
Repeat for each device you want connected.
If you can't find an obvious problem, start testing the network with pairs of devices plugged in.
Also check for subtle things, like two devices trying to share the same IP address.
And a side note: when you are reduced to checking single entities for sources of error, remember that your Ethernet cables can themselves be sources of trouble, as can specific ports on the SMC box.
(no subject)
Unplug all but one machine.
Debug that connection.
Repeat for each device you want connected.
If you can't find an obvious problem, start testing the network with pairs of devices plugged in.
Also check for subtle things, like two devices trying to share the same IP address.
And a side note: when you are reduced to checking single entities for sources of error, remember that your Ethernet cables can themselves be sources of trouble, as can specific ports on the SMC box.