If you go by the hivemind thing, the aliens are aware of the danger the Predators can be due to the Queen's memories on them.
There are aware of how much violent Predator are and the threat they can be towards their kind in comparison to other species, there might be anger and revenge feelings to it so even one is running away and not doing anything dangerous it wouldn't matter due to the history between them. The Queens that were used in the rituals are probably really pissed off. Is it like prejudice from the Aliens against all Predators?
Those 3 preds were not the ones responsible for what happened towards the Queen, they are just kids thrown into violent challenge to man up. Maybe one of them didn't even want to be there but they were punished regardless, regardless the deaths of everyone involved was just collateral damage of the system that Predator clan created.
Maybe increasing their numbers first, even to that extreme was a strategy for the aliens to make sure the Predators wouldn't stand a chance and that the Queen would be easily free. They had their plasma casters already, relying on numbers was their only chance.