You should not use one reciever for two controllers.
Usually you can use two recievers on one sensor, but depending on how far apart your controllers are, both recievers will need to stay within line of sight of your transmitter. And yes, you will probably have to purchase two sets of units because that is usually how they are sold.--Unless you buy through a third party website rather than the company or distributor (not really reccommended). Basically, buy the two sets (2 transmitters and 2 recievers). Try pairing up one sensor to both receivers, following the directions in the manual. Test it. If this doesn't shut down both controllers, install the second transmitter as you will already have it. If it does work with one sensor, you can just store one of the transmitters until the one you use first dies out on you. Usually the transmitter will die out before the recievers, so you will have a backup on hand.