Yes and no is the answer. People want to know because they are thinking about adopting two cats together so they have an instant companion for life. Jackson Galaxy advocates adopting two cats from a shelter provided they get along. It is a big advantage to a cat owner particularly if they are away from the home quite a lot. Note: there is no substitute for the human companion, however, provided they are good at it.
Getting two kittens from the same litter is a good choice because they are great companions and playmates when growing up. Their relationship may cool as they become adults and sometimes the relationship descends into one of incompatibility to the point where they hate living with each other. This may lead to signs of anxiety and stress such as defecating outside the litter box, urine spraying, scratching walls and furniture and fighting. Cats like humans develop their own personality and they become independent demanding their own home range (their territory).
So, adopting siblings as permanent companions can be a failure. I don’y have statistics telling me the success rate. I adopted my cat from a cat rescue organisation. The woman there said that siblings fight. That must have been from first hand experience. She was partly correct. They might fight and they might get on.
My ex-wife and I adopted siblings: a male and female. They were great buddies through kittenhood into adulthood and as adults. Success. We divorced. Drat. That split them up. I think we should have agreed to keep them together. I was less savvy about cat behaviour and guardianship duties back then.
I believe the only way to be sure if siblings get on, or any pair of cats for that matter, is to suck it and see. Test it and try it out. But you have to have the facility to take one of the cats back if it fails. Separating the cats permanently may be the only answer if they are hostile towards each other. And that can be traumatic for the owner.
