The LNB is capable of processing the signals from either the even numbered satellite transponsers or the odd numbered transponders, depending on the polarization it uses. The receiver tells the LNB whether it wants access to the evens or odds, depending on which channel you've told it to tune in to. This is why you needed a dual LNB for two receivers - if you had them both hooked to the same LNB, whenever one receiver changed the LNB polarity, the other one would go along for the ride, whether it wanted to or not, or they would do battle continually switching back and forth. A dual LNB is just two units sharing a common housing, so each receiver can have control of its own LNB.

When you want to connect more than two receivers to a dual LNB, you can do it by hooking up a "multi-switch" between the LNBs and the receivers. The multiswitch keeps one side of the LNB at one polarity and the other side at the other polarity all the time, so that signals from all the transponders are available full time. Then it switches the connection for each receiver back and forth between the two LNB sides, depending on the channel each receiver requires at the time.