They were adopted separately, so not the biological siblings, but they get along like a big brother and a little sister. My daughter took this picture when they were locked up fact to face, kicking the heck out of each other on the couch. XD They momentarily stopped when the first flash went off (*WTF!?*) and the result is this "Awww, they're hugging each other... So cute." pic.
The orange and white one's name is Fanta, the big brother. (He looks kind of like
kogepant chan's Tenki.) Grey and black one is Twinky (sometimes called Dvinky, Boinky, Baby, and other names). The very feisty baby of the house. They have a grey and white handsome older brother, Midna. (Got the name from "The Legend of Zelda: Twilight Princess". When we first got him, we thought he was a girl, thus the name. Two weeks later, my daughter comes to me, saying, "Mommy, something's growing on Midna's behind..." XD)
Both cats play fetch (not with each other, though. LOL). Twinky likes to jump on my tablet and show off her angry skillz.