The difference between API mode and AT mode is the type of data being sent and received over the UART. In short, API mode is a Frame based interface using Intel Hex frames where as AT is transparent…
Are the sensors connected to the radios UART or ADC lines?
Sleep mode is used on an End device. If your device does not need to conserve power, then there is no reason why it could not be an always on Router.
As in Mention Earlier i want to send data form multiple xbee(end device ) to Single xbee(Coordinator) which is connected to Computer.but i cant send msg simultaneously otherwise end devices create interference…
You can see how to configure the XBee modules for cyclic sleep by following the directions in the manual as well as http://www.digi.com/support/kbase/kbaseresultdetl?id=2193. I would suggest not using sleep modes for this and just send a broadcast message.