Some things I can think of:

- Try getting one device to work. Then add the second, and then the third. Troubleshoot one step at a time.

- The last device in the chain needs to be terminated, either by the last device (if it has built-in termination) or by a physical terminator connecting to the open connector on the last T.  If it's built into the last device, don't use a T.

- Make sure no there's no internal termination active in the devices between the clock source and the last device.

- BNC T-pieces and cables can sometimes be faulty; they connect internally mechanically, rather than being soldered. Try pushing the end pieces together.

- Make sure all your devices are compatible to the master clock speed you want to run at, and set to the proper internal settings for them to sync. 

I find this WC stuff very fiddly and really good connectors are not easy to find or cheap. I have 4 devices synched this way and sometimes if someone jumps too hard in the CR, the clocks will momentarily go nuts so I've got an issue somewhere...