I've seen a similar issue with the cats we had when I was a teenager. They weren't siblings, but the older one would bully and harass the younger one (to a point of denying her access to food or the litter box), and would actively hunt her.
In the end, we managed to get her to stop her bullying, but she never interacted with the little one. A truce is the best we could accomplish.
Reading between the lines of your question, I infer that you treat both cats with kindness and softness. That's my assumption, at least, based on how you phrase a few things, e.g.:
Oftentimes, he will come between Cila and our hands, claiming the touch for himself.
A stolen touch should not be a touch. If you allow him to steal attention, then you are telling him it's okay to steal attention.
Do not allow him to actually get pet when he is stealing from her. The moment he cuts her off, you should pull back your hand, and offer it again to her. He will likely keep trying, but you should keep pulling away your hand. Be consistent and stubborn.
I tend to add a verbal cue. I would pull away my hand, look him in the eyes (blank or annoyed stare) and say "No." (like a strict teacher). If you're consistent, he will associate "No." with doing something bad, which should get him to understand your feedback faster after a while.
If Cilek has walked away, do not pet him. That will only teach him that he can drive her off and take the attention for himself. Instead, completely ignore him and don't even acknowledge him. This makes him realize that he ruined the moment (for both him and Cilek).
Over time, the message will become clear: If you refuse to let Cilek get attention, then I will refuse to give you attention.
If he allows you to pet Cilek, and he does not cut her off, reward him. Give him a pet, and make it clear that the second pet is addressed to him. Keep alternating between the cats. Whenever Muskot tries to cut in line, deny him the opportunity.
If you notice that he has trouble understanding who you're trying to pet, it might help if you say the name of the cat you're going to pet. Even if they don't register that as their own name, he should eventually notice that he never gets a pet when you say that same word ("Cilek").
This is just an example of how to deal with "douchebag" behavior. Don't berate Muskot for misbehaving (he might not be aware that he's doing something wrong), but attach a consistent consequence to his misbehavior. He will learn that his behavior always leads to the same (unwanted) consequence, and should stop behaving this way if he wants to avoid the consequence.
However, I get the feeling that this has gone on long enough that Cilek is deeply affected by this.
- Cilek runs away from him and does not want to eat next to him.
- She struggles to go to the litter box because she has to walk past him.
- I have to take her food to her bed, otherwise she won't eat.
This is the same pattern as what happened to our little one. She got bullied day and night for simply being present, to a point where she was afraid to live in her own home. It seems that Muskot has been doing this long enough for her to prefer leading a life of banishment (basically only being master over her bed) because of how Muskot treats her.
This is an abusive relationship. This is the feline equivalent of domestic abuse, which revolves around controlling people through their fear of you.
Muskot may not be aware that his behavior is abusive, but he needs to understand that his behavior is not acceptable.It sounds tough, but the best way to stop a bully is to make them the victim (so Muskot understands what it's like to be Cilek).
You need to actively punish Muskot for his behavior. The punishment doesn't need to be severe, but you should punish him in a way that makes it clear to him that it's an unavoidable consequence (caused by his behavior).
I've always used an escalation pattern.
- Strictly say their name, to get their attention.
- Strictly say "No". (this won't mean much to them in the beginning, but after a while they will associate this word with your negative feedback)
- Use a spray bottle to spray some water in his direction. You don't need to drench him or even hit him, you simply need to inconvenience him.
- Physically (but calmly) remove him from whatever naughty thing he is doing (if he doesn't like being picked up, then that is punishment enough). If he walks away when you approach him, don't needlessly chase him (he already removed himself, his compliance should be rewarded by not escalating it any further)
The approach is always the same. Start from the top. If he ignores you and continues, escalate to the next step.
Over time, you'll notice that you need to escalate less before he (voluntarily) yields to your feedback.
Our cat got the spray bottle for meowing incessantly when sitting by the window. It took him about two weeks. By then, he didn't even need the spray bottle anymore, if he heard me move on the couch (which meant I was reaching for the spray bottle), he would shut up.
I was the only one in our family who used the spray bottle, and there was a notable difference in how he responded to my voice compared to those of my parents. When they called his name, he wouldn't stop (or only for a few seconds). If he heard my voice, he moved away from the window.
Note that I didn't make him afraid of me. He still slept with me on my bed at night, and played more with me than my parents. He did not avoid me just because I'm the one who told him off.
Don't scream at Muskot. Don't treat him like he's knowingly misbehaving. Don't overreact. The intention is not to make him fear you. The intention is to inconvenience him, to a point where his choice (bullying) does not gain him any benefits (being the boss).
The most important part is that you are consistent in your approach. There must always be a negative consequence to his behavior. If you only punish him some of the times he misbehaves, he won't realize that the misbehavior and the negative feedback are connected to each other.