Cloud and Midnight have fought in my sewing room, and had stand-offs in the living room and kitchen. This just started about a week ago. They are 11 months old. Why would two boys be this way if they are from the same litter?

Maybe territoriality is more important to them than brotherly love. Not all cats get along just because they're from the same littler, I don't think.

They will get over it. They are deciding who is going to be the top cat.

Sounds like they have become adults and are fighting over who is the alpha cat.

Make sure both are neutered. They may just be playing really rough--some kitties do. Or fighting for dominance. Cats don't have "brotherly love". As adults, that's a human thing. If they really are fighting "for real" it may be time for either behavior modification, or finding one of them another home. But my first guess is that they play really rough, and then one or both get mad and accelerate the fight. Now THAT is something siblings do!

Yes, that was my question, are they neutered? If not, sounds the the testosterone has hit! lol

Our boys are brothers, they are neutered AND they still fight like hell cats. A few minutes later, they groom each other. It is a way to establish who's the top cat. With us it is Monty and Mr. Bean is the bratty "I can beat your butt if I want to" wannabe. It is hysterical to watch them stalk and terrorize the house.

People always come to me and say theywant to adopt siblings so they will love each other more. I tell them cats are not like that. They can be from five litters and all love each other, be from the same litter and not want much to do with each other. Fixing them is key. Get a bottle of water and squirt them if they get into it and yes they are setting up who is going to be the dominant one. They most likely are making noise and slapping at each other vs kicking each others rear right? Keep their nails short so if they do go for it no one gets a serious injury. And for the most part soon one will be the leader of the pack and its all done. That one will get food first, use the litter box first and pick the best spot on the couch or your bed. You cant change that they will work it out on their own. Hard to watch however.

why do people insist on believing animals have human emotions??????
is it all the cartoons kids have watched over the years of talking rabbits, pigs, coyotes or what??

or the Disney lovey dovey stuff that shows a made up dinosaur lovingly tending it's babies ??

a cat is a cat is a cat - especially if they aren't fixed - if they were brother and sister and not fixed you'd be having lots of little incest babies around and the cats wouldn't care less or even KNOW it wasn't "right"

I just re-read the posts and I do not see what you are seeing. I only said that they were from the same litter. I am sorry that I have upset you.