Hi all!

I have 3 cats, 2 females both aged 11 and one male aged 7. He is a pure breed Maine Coon.

The problems I am having with him is that he is extremely demanding. He wants my attention at any cost and will do anything to get it. I work from home so I am already giving him the maximum attention I can give but it's not enough for him. If I am sitting at my pc and am busy and for a change do not have time to pet him, he will get really aggressive and start attacking one of the girls. He's quite big so I feel sorry for her and get up from the chair to "rescue" her but at the end of the day all I'm doing is giving him what he wants - attention.
He will come and lie on my keyboard even after half an hour of me putting him back down, he is very persistent and won't give up so easily.
He had a phase where he would pee next to the litter box if I ignored him. This he stopped now (though he does this in phases) But something else that I found strange was that once I switched the litter boxes around and he didn't like that so he started peeing next to them until I switched them back into their original place?!?!
Anyhow my main problem now is something else he's started about a month ago. Besides him attacking one of my girls, or meowing the house down, he now BULLIES my cats of the litter boxes! As soon as he hears one of the cats go on the box, he will dash there just to get them off. This is so confusing to me because they've been living together for 7 years, so why is he doing this now?

I am trying to give him more attention when he's being good, lying around somewhere I'll sit next to him and pet him etc... this seems to have calmed his meowing down a little but he still gets his phases of aggression.

When it comes to the medical aspect of him, it gets a little complicated. When he was about 3 years old, he started shaking. He would just sit there and shake and it looked like every once in a while he'd get a cramp. I took him to the vet who sent me to a heart specialist, who then had me give him 3 types of medicine. After a few weeks my cat would not even eat food anymore, let alone puke out all the medicine. He had lost so much weight because of it that I decided to stop it all because it was going to kill him. The doctors said that there is nothing much they can do and for me to see how things go. Great. Anyhow at that point I decided to give him even more loving to try to "heal him with love" so that maybe now I've created this spoilt cat?
He has been ok with the shaking overall, but he does get it sometimes but it's definitely not as bad as it used to be years ago. I obviously don't know what's causing his shaking but I could imagine it's also stress from his side.

I hope someone can help me because I am expecting a baby in 2 months and the only thing in my life that is causing me grief is this cat when he gets into his bad moods. Otherwise he is the most adorable sweet thing and I love having him around.

Also, he is generally a shy cat, hates sudden noise especially the doorbell where he'll go and hide for hours. Also very vocal when it comes to him wanting food, different food of course than he's already got. But then if I walk with him to his food he'll sit and eat it, as if he needs me to see that he's being a good boy and eating his food...

Let me know if you have any questions or if I've left something out.
Thanks!