This.You have to watch them. I would never house the two of them together in a tiny coop/run setup unless you can be out there to open the run before any of them come off the roosts in the morning. That is great recipe for a nasty fight.
Even if they don't 'fight to the death', you will constantly be in a situation where you have to doctor injured birds. I agree with @Eggcessive that more "gamey" bantams are typically more likely to be male to male aggressive and IMO your best option is to rehome one of the boys. It will be easier for all involved.