Can I play two patches at the same time?

No, you cannot play two patches at the same time.

You need to have both your organ and your piano channel strips loaded on the same patch. Then, assign each channel strip to the keyboard that you want to do. In certain cases, you may have to go to the Layout mode and assign a separate channel to each keyboard, depending on how you are setting up your equipment (may not be necessary for you).

See this screenshot for an example of what your MainStage concert could look like to achieve this:

You can combine the two patches into one easily.

You can create a patch by combining several existing patches. The new patch contains all of the channel strips of the selected patches.

Create a patch from several existing patches

1. In the Patch List, select the patches you want to use to create the new patch.
2. Choose Create Patch from Selected Patches from the Action pop-up menu at the upper-right corner of the Patch List.The new combined patch appears in the Patch List, labeled “Untitled Patch.”
3. Double-click the name and type a name for the combined patch.