Hi Jules
What I have interpreted from your doubt is that you want to dedicate only one PORT for interfacing light,proximity and temperature sensors, also you might be using ADC concept with this, is it so? If yes, then of course you can do this. There are many ways of performing the same but the main idea lies in multiplexing these sensors. You could use a multiplexer (4:1 in this case) or make your own using BJTs, I would suggest you the former. It is simple, the output pin of multiplexer will be connected to the input pin of ADC IC like ADC0804/08/09. The three sensors will be connected to individual input pins of the multiplexer. You'll also need some I/O pins as selection pins for multiplexing.
This might help.