I had problems when I kept sex linked hens too. They do seem to need extra protein, more than a layer provides because of their higher production. They also seem to be a bit mean to me, but others keep them without problems. Thankfully there's all kinds of breeds to choose from.
Depends where the yolks were. In the reproductive tract where they belong or in the abdomen where they don't. Generally if they had yolks in the reproductive tract they were laying. In the abdomen, they were internally laying which is often deadly due to the infection they cause.
Aggression can...