These two kittehs were found together as adults by the local animal shelter, where they lived for over 6 months in a tiny cage (let out for R&R, of course) before we adopted them. They are presumed to be brothers.
When we first brought them home, they were inseparable, walking shoulder-to-shoulder through the house and sleeping curled up together. We had trouble telling them apart. Within a few weeks, we figured out their differences in markings. We called them the “herd of cats.”
After 6 months, the big one developed “littermate syndrome,” an advanced case of “you're not the boss of me” and sibling rivalry. It got intense, to the point where we considered rehoming one of them for the little one's safety and peace. I've so very rarely had to rehome an animal, and never a mammal. When I adopt an animal, it's a lifetime commitment.
A while later, the orange cat (see other kitteh pics), walked into my office space while I was writing and thus came home to live with us. Orange cat is an overgrown (ahem, rather so) toddler, and he started jumping on the big cat “to play!” At which point, the big cat lost his shit because he was so focused on the battle for dominance and territory. The rambunctious orange cat became his nemesis, a social position that the doofus orange cat does not care about or probably even understand. He just wants to play, which is why he leaps out at the big gray cat constantly.
And thus, the littermate syndrome situation was (mostly) defused, and the two twins can now share a windowsill and look out at the early summer morning together.