my goal is to consolidate sources to multiple outputs not to separate them.

Works the same way, just in reverse.

Put the following in ~/.config/pipewire/pipewire.conf.d/10-virtual.conf

context.objects = [
    {   factory = adapter
        args = {
            factory.name     = support.null-audio-sink
            node.name        = "Virtual-Sink-1"
            node.description = "Virtual Sink 1"
            media.class      = "Audio/Sink"
            audio.position   = "FL,FR"
        }
    }
]

If you need more than stereo, you can adjust it in audio.position. If you need multiple devices, just copy/paste the block between the {} multiple times and rename the device.

After that restart your system, you should now have a new audio device called Virtual Sink 1, select it as default device.

Start qpwgraph and connect the Virtual sink(s) to your output device(s) by dragging the monitor nodes to the playback nodes:

You can now try if everything sounds correctly. If it does, hit Ctrl + S in qpwgraph to save your patchbay somewhere. It will save all the connections you just made and establish them on start and on the fly if new devices are added.

Next up, add an autostart entry for qpwgraph. This depends on your desktop environment, add the --minimized flag so you don't see the qpwgraph window every boot. You can also select "Start minimized to system tray" in "Graph" -> "Options".

If you only need certain applications to go to both devices, you can also achieve this without the virtual device by just dragging your application node directly to your bluetooth device in qpwgraph and saving the patchbay, it will route the audio automatically every time the application starts.