First, the key is easily cut at any ACE hardware because it is only to open the driver's door.
If you bought the car from a Nissan dealer far away, maybe you can go to a Nissan dealer that is close to you, and the far away seller can make a deal and have the close dealer done for you free?? (Nissan professional courtesty?)
I would replace the battery on the nonworking fob and see if it opens and closes the doors. (since the key was from a different car, then very likely the fob will not work).
If the car does not respond with the new battery, then go to Ace or a locksmith. They have a machine that tells you if the fob is putting out a radio signal at all. You can press the buttons on the fob, and it will tell you if the fob itself is "working".
When you have working fobs that you want to program, you need to go to the locksmith with ALL the fobs you want to program and...... THE CAR. The locksmith needs to plug in a computer to the car, call Nissan for codes, and program the fobs... It may cost $100-150 for the locksmith to do the programming, depending on how greedy he is..