Problem with multiple drakes together- advise please

I started having problems a couple weeks ago. My questions are at the end, but this takes a little explaining.

My poultry/waterfowl are separated into three groupings (three pens in the house each opening into a pen outside) so they all get along and this WAS working.

A few weeks ago, the 5 drakes (who have always had raging hormones-they often chased each other around) "went after" the goose (whose sex is not known yet- it is abt 8 mth old and really large). I came home from work to find the goose with feathers missing from its neck, and one eye badly damaged and the other eye didn't look great either. I know it was the drakes that did it because they were still going after the goose when I arrived. The goose is so much bigger than them I was surprised this happened and it didn't seem to defend itself at all. I removed the goose to a cage in the garage to heal a bit, kept its eyes clean and used an antibiotic ointment for animal eyes. It is recovering nicely so far.

Then, we decided to "rearrange" because of what happened, so the 5 drakes went to a pen with just 6 large breed chickens. That WAS working for abt 2 weeks. Then this morning I went out to find one of them dead. It was half out of its pen inside their house through a seam in the chicken wire. I think (now in hindsight) that the other drakes "went after" it, but I am not sure. It was missing neck feathers and looked a lot like the goose did after they got after it. But it could have been from being stuck maybe.

Now tonight one of the drakes wouldn't go in the house. Every time we tried to get it to go in, the other drakes "went after" it. Finally we had to take a cage out to keep it safe from the other drakes for tonight. But tomorrow I need to build it a pen, as the cage is only big enough for a temporary solution.

I can't put it in any of the other two areas due to compatibility issues. I doubt this is a pecking order issue, as that would have been worked out by now (they have been together 8 mths) and not so violent. All I can come up with is that it has started because they are reaching sexual maturity, and probably won't get along anymore.

I thought (perhaps wrongly) that as long as there was no female in the equation, there would be no problem. Do drakes fight like that if there isn't a female to fight over? Ideas? Anyone have any insight about this kind of behavior? I would really appreciate any info you might be able to offer. I just want to know for future reference so I know how to group them.

Thanks!