They are joined at the hip, figuratively. Everything that one does, the other has to do. Eating, sleeping, playing.. everything. (Almost everything... They quickly learned that the litter box is one cat at a time only.)
It's almost like owning just one cat, just with double the poo.
I genuinely believe a second cat is the greatest thing you can have for a cat (as long as they get along good).
If you have the space I'd get a second box in the future.
We adopted a brother and sister cat and it's well worth it in my opinion, they keep each other entertained. They also love each other more than I thought was possible lol.
That's how they get you, these... cats. Devils more like it. It's all purring and mewing, and then Bam! one of them hits you with a head nudge. By then, it's all over. Soon it's the expensive food, and the water filters, and the fancy kitty litter. Before you know it, they are asking if their brother can crash on the couch. You know, just a for a few weeks. He's got an idea, and it's gonna be huge, like Facebook huge, but he just needs a little bit to get him off the ground. A year later you are laying in bed at 4 AM looking back on the choices you've made, wondering how it ever got to this point, and you feel a sharp pain in your gut. It's one of those furry devils come to ask for more food, or to warn you about the spider it thinks it saw in the hallway, or to tell you that the vase above the TV is haunted. It doesn't matter. You love them, anyway. You're all theirs now. Under their spell. They call it love, but it's spelled t-o-x-o-p-l-a-s-m-o-s-i-s.
i recently also adopted a bonded pair and it's such a good idea. the scaredy cat of the two settled in really fast since he'd be hiding and then see his niece walking around getting pet and purring (not being attacked by the terrible humans who stuck him in a box just the other day) and he'd poke his head out.
plus, you're always getting to walk into a room a find them cuddling adorably. it's great!
Fenn still likes to suckle when he is going to sleep.. Mainly on his brother. After that, Sudo is usually drenched in slobber so both meanings work. :)