I have had my neutered cat Frankie (The larger one on the pic) for three years. I then rescued a barely 6 weeks old Tuxedo Kitteh Yoda (The smaller one on the pic) from being tortured to death by some kids and brought him home.
He was sooo tiny but Frank wanted to skin him alive, he was so upset there was another feline on his territory he just wouldnt shut up. I took a week off work to get them to calm down and on day 5 they were sleeping next to eachother purring away like best friends forever. I still have them both and they have become really close, when i take one of them to the vet the other one is heard meowing when i close the door behind me.
The fighting and the violence Will stop after a maximum of 10 days after which they will be buddies. The fighting is a process they need to go through to establish authority over the territory. When they play-fight though the kitten will often be really screamy but thats just their nature, its not like the big one is killing them. Been there, done that also :)