Regarding fertile eggs: I'd suggest that you do a thread search on how to tell if an egg is fertile (before being incubated). A person who has not been trained in what to look for would not be able to tell the difference between a fertile egg and an unfertile one. Enjoy your eggs whether they are fertile or not.
Re: rooster behavior: It's normal for young roosters to be aggressive to each other. They are sparring over who gets to be boss. Sounds like big roo won those rights. It's also normal for young roosters (cockrels) to chase the pullets, and to be a bit selfish when it comes to the food/treats. More gentlemanly behavior will come soon. The way a rooster mates looks brutal to us humans. He will grab the hen by the back of the neck, and pin her to the ground while he does his thing. She may squawk, but then she will get up and shake herself off and go about her business as though nothing has happened. A good rooster will mature to: Watch sky and land for danger and alert the flock. He will tid-bit the girls. (He'll find a morsel and may repeatedly pick it up and drop it while making excited clucking noises. When the hen comes, he'll share his morsel with her.) He'll dance for the girls before mating. (Dropped wing, rapid stepping in a semi-circle around her, maybe while clucking) He may even accompany his hens to the nest box, and may even climb in and fluff up the bedding for her, while clucking.) He will never be aggressive to the chicks, and may even help raise them. He will be people friendly: will never attack a human. That being said, I'd take every precaution with a rooster, and keep him penned when young children are visiting, and if it is necessary to administer care to one of his hens, I'd pen him up first.
I do not think big roo had anything to do with the death of little roo. Perhaps, indirectly, little roo did break his neck while sparring, but if so, it was a congenital weakness. He could have died from any number of congenital causes. I'm sorry it happened, but, you still have an other roo. Are you planning to raise your own chicks? If you find it stressful to have a rooster, you certainly are not obligated to keep one.