There are two things you can do:
The most important thing you could do is definitely get Snowballs fixed. Definitely - without a doubt, because this is most likely what is causing Rufus to become so viscious. As he still has his goods he is producing a lot more testosterone and so Rufus, sensing this, feels he has to man up to face the challenge.
And there is this product you can buy from your vets (not sure of the exact name) which you plug in to the wall and it sprays out the hormones that mother cats release when their kittens are young, thus calming them.
I have four cats, two of them hate one another but we only have the occasional tiff between them, they never take out on us (if they did they wouldn't be fed !). But seriously, just give it time, try getting Snowballs fixed or getting the spray and everything should work out fine