Each LNB either dual or single, can only pick up 1 satellite signal. Dual just means you can hook 2 wires to go to 2 separate receivers.
What I don't understand is, you said you are getting both Nimiq 1,3 and Nimiq 2? This is not possible with only 1 LNB. You would need 2 LNBs to do this. Also, you would need a switch to do this as well. And, a special bracket or a dish that skews (tilts sideways) in order to acheive 2 different satellites all at once as they are in different posistions in the sky.