As someone who has owned multiple cats and a dog, I can say it really depends but in all, both will get used to each other. They won't fight, hiss or bully other pets in the home if they're from the same parents, but will instead be more prone to look after each other in ways like cleaning and playing. When my cat's sister had died and we'd 'replaced' her with a kitten, the original house cat was annoyed by the new addition, but didn't go out of her way to severely harm her. Beth - the first one - eventually got used to the kitten Smudge, and they got along together pretty well and shared toys, food and places to sleep. When Smudge died, my mum's partner brought his aged dog around which at first didn't get along with each other, but when Beth scratched her across the nose, it was clear she was tired of running in vain on a laminate floor. The dog was even scared of Beth and sometimes just wanted to play, but Beth constantly taunted her by brushing her tail near Cassie - the dog's - nose. And you're not the only one who feels suspicious if I say that Cassie later died, but Beth remained chubby and healthy.
Just some anecdotes there for you. It really depends on the cat, but I don't know any that would bully another for a lifetime, especially if it meant separation and being forced out of the house for a short while while the other got attention. I'd recommend you get two because cats don't do that much when on their own - when they get older they moan a lot and just don't want to chase loose pens, small round object or string that much. Whereas with company they manage to stay quiet and occupy each other. I've noticed that having two cats lessens on the noise, because the other might distract the first if they're hungry, want to go out or just bored.
I hope this helps! ^^