help me for LTC2414

hi

whit above code the output data varies...for 5v the output is 0.0043021v....& for 3.3v is -1.545451.....& for 0v is -2.5v

above program has just one channel (ch0),now if i want to have 2 channels(ch0 & ch1) whit 0 to 16777216 output data ,what should i do?
thanks