How do I make my cats get on?

When they were kittens my cats loved each other. Played together, slept together, it was wonderful.
Now they fight every day.
I think I blame the boy for starting it as he likes to jump on Tilly and bite her back and bum as she sleeps. He likes to chase her all over the house. She then hisses and rolls on her back. He freezes, and slowly moves towards her until she loses her nerve and flees again.
She has now started taking pre-emptive action by whacking him in the face if she suddenly comes face to face with him. At those times he usually had no inclination to chase her and looks incredibly startled and a little baffled at being attacked for no good reason.

She broke her leg a while ago, and we bought feliway, and vanilla-coated them. It worked for a while, mostly because she'd been confined for ages, and was so happy to see another cat she didn't care that it was him. However, as she regained her old personality, and he got over the novelty of being allowed into the living room again, they reverted to as they were before.

They're both lovely cats, and we're all so sad that they don't get on any more.

Is it normal for one cat to like sneaking up on the other? Can I make him stop?

I'm assuming they are neutered and spayed. It sounds like normal cat play. Charlie and Ling STILL do that - wrestle with each other. Males are more likely to initiate the "dominance" actions.

Just keep their nails cut and if it gets too much, just break it up and clap your hands and tell them NO

They're both s/n.

I mostly feel bad for Tilly. She's started sleeping in all the hidden nooks and crannies she can find, otherwise he disturbs her sleep.

Maybe I should get a more interesting toy to distract him when she's had enough.

What you say is a perfect description of the relationship between my Mellie and my Twinkie. I think the key here is whether or not she's afraid of him. It sounds to me like she's holding her own pretty well. If she becomes afraid of him -- avoids him, hides from him, runs away from him, slinks around the outside walls, is afraid to use the litterbox -- then you've got something to worry about. But as long as it's pretty even, then it's just something that's, well, that's the way it is. I like to think of a brother and sister. They love each other but can't stand one another and are always fighting about something.

What's really funny with Charlie and Ling is that as soon as we come home from a show, Ling is right there to give kisses to her brother. Within 10-15 mins they are back to wrestling and "leave me alone" stuff.....

They're pretty evenly matched, but they never have the 'love' bit of a love/hate relationship. They either ignore/tolerate each other or bicker. But they never seem to actually hurt each other, so I'll live with it.

Mellie and Twinkie got better, and are still getting better. One day they were even sleeping together on my bed. A mound of laundry separated them, but still, they were sleeping closer than they had ever slept before. I think your cats will be OK.