It is hard to figure out what you are saying, but I assume you mean there are two 14/2 or 12/2 cables coming to your existing vent fan.
The way it was probably wired before was one of the white wires is the neutral, and the rest of them were all switched hot wires.
If you have already taken the wiring loose you are going to have to figure out which cable is which.
If you haven't taken the wiring loose already, and you can't figure out what wire is what, call someone else to do it for you.
First make sure the breaker is off by testing at the switches and at the vent fan. If you are using a non-contact tester make sure to test that it works both before and after you use it to ensure the breaker is off. Go ahead and put a piece of tape over the breaker handle to indicate it shouldn't be turned back on.
If you do this part incorrectly you will have a dangerous situation.
Short out the leads of one of the cables at the vent fan. If you didn't do the first part correctly you will have a spark.
Use a multimeter with a continuity feature to find out which cable is which at the switch box with all of them off. ( If any of them are on you may get a false positive )
Mark the neutral that goes to one of the switches with electrical tape at both ends. ( any color but green yellow or white, usually black or red ) Now it should be easy to figure out what wire goes to what switch, and which one is the neutral.
After you know which wire is what, go ahead and wire it up.
If you can't figure out which wire is which, get someone else to do it that knows what they are doing.