How did you insert the synths into Sonar.
Let's sort the basics out and the rest should straight forward.
By far the best way is to simply drag the synth from the Browser into Track View, when the "Insert Synth Options" page opens, (if it doesn't, click the "Insert Synth Options" in the browser and check "Ask This Every Time") make sure ONLY "Midi Source" and "First Synth Audio Output" are checked.
Now route both of the AUDIO track's output to your master bus. You do have a master bus yes? If not, go and create one.
Record/Type in some Midi and you're good to go.
You might want to enable Input Echo on each of the Midi tracks to hear everything, though it's not always necessary.