Hi,
You know, I'm getting the impression that all of this is really just rough play. The other day, they got into it and I saw Elvis (the older cat) pin Danny down a few times and bite him on the back of the neck. I was really scared that he was hurting him, and when they stopped, I picked Danny up and examined the area, but there was nothing. No blood, not even bite marks or a scratch. I don't think they're really hurting each other. When they started these fights, Elvis got two scratch marks on his nose, but they have healed up and there haven't been any more.
I have also noticed that sometimes, when Danny is napping, Elvis will go up to him and start grooming him. It's so cute. I wish they could just be that way and not have these fights/rough play sessions. I really hope they're only playing.