Yes,
4 channel ADC should have four input lines for four different analog signals (single ended or differential). But you have to control it's opperation in a way to select which channel to use for a a/d conversion you are going to initiate (ok, there are some smart parts that scan inputs automatically after appropriate setup is done).
a 4-channel ADC is actually one ADC with a multiplexer. You can connect 4 signals to 4 different pins, however, you can only convert one channel at a given time. The 4 channels have to be converted serially. If you have a fast ADC converting in 4 usec, all 4 can be converted in 16 usec.