What model TC and how old is it?? The actual model number will help, A1xxx from the base.
See https://discussions.apple.com/thread/6324708?tstart=0 for how to find the number.
The firmware revision could also help.
And the network layout. Is the TC the main router in the network?
Screenshots help no end.
Simple solution.. start over. Factory reset the TC.
Please do not use apple recommended names.. use names that are short, no spaces and pure alphanumeric.
Use WPA2 Personal security and a pure alphanumeric password of 8-20 characters unless you are paranoid.