Excessive Fighting

So we our budgies gave eggs from which 3 children came out and 2 ofcourse made a pair and the third one was a boy left he was severely injured by the couple[siblings] and his leg is broken. Now the female from the couple had died like 2 weeks ago and we had kept both the male budgies together but now the one from couple has started beating the one with broken leg.. He beats only when we are not around. So what we do as if we keep them alone then it is alot problomatic as this may increase their stresss.