Well, not exactly what you were asking, but... We have two kittens who are similar to that, only they don't look THAT attached to each other. They like to play together, clean each other, sleep together... But not always and they don't spend like, ALL the time together. They both need time for themselves too. They're indoor cats but we plan to let them be outside too when they get older so I decided to take them outside separately and show them around. I left the main door open, closed the corridor door and took Tim. I could hear Lena, the other one meowing and scratching on the door for about half a minute. And then...
That was the first time our Lena managed to open the door by herself. That's all