Use the barrel as the bearing that the fake barrels rotate about? I suspect that is what you were planning.
Looks like you've got a 1" or so hole in the barrel holder, so put a piece of 3/4" PVC through that, your barrel runs through the center of that pipe. Neither the barrel nor the ~3/4" pipe rotate.
The rotation mechanism and the vortex mechanism are behind the barrels, where the loading and spinning mechanism would be on a real minigun.
If the 3/4" PVC isn't stiff enough to support the weight of the moving barrels then try similarly sized steel pipe. This assume you are going for a "minigun" look and not a "Gatling" look.
If you don't even want to bother with trying to get the central pipe to support the load, then set it up like the original Gatling gun, which has external braces running from the breach end to the barrel end.
In the photo you can see the external braces that support the rotation point at the front of the barrels.
If you can find a bearing that matches the OD of the central PVC (or iron) pipe that would be the best way to reduce friction. Two bearing, one at the front and one at the back. A pair of bushings for each bearing so the multibarrel assembly can't move front to back on the central pipe.
To hold the real barrel inside the central pipe ...
I would first see if you can get lucky and find a wood dowel with the same OD as the central pipes ID. If you can get a dowel that is just a bit oversized it can be sanded down to fit. Cut the dowel into ~1" lengths and drill a hole in the center for the real barrel. A couple should be all that are needed to support the barrel in the central pipe.
If you can't find a suitably sized wood dowel then just cut wood squares with diagonal = central pipes ID to use in place of the dowel.
Fiinding suitable bearings may be a PITA. McMaster probably has what you want but your local hardware store probably doesn't. You might be able to get away with homemade non-roller bearings. Just a piece of copper pipe that snugly fits around the main inner pipe. Get the smallest ID copper pipe that is larger than the OD of the central pipe. Cut a 1" length then slice the cylinder open to make it look like a "C". Remove enough material in the slice so the C can be clamped down fairly snug onto the central pipe. Capture that C in your barrel holder. A bit 'o grease and the ghetto bearing should last quite a while.