They probably didn't really need a word for it. If they were being fair about terminology, brother was a bit on the too-simple side anyway. They were a lot more than two adopted kids from the same family anymore, and had been for a long time now. And this -- this only furthered things more. There was no point in inventing a new language for two people who already knew what was going on.
He'd seen a million kisses before - from Klaus doing it, to people doing it in the background to just random stuff in movies. It was inevitable, seeing stuff like that. But doing it was infinitely more interesting. It wasn't like he was clumsy at first or anything, but it did take a few seconds to really melt into it, to figure out exactly where he fit and at least begin to start figuring out how it could be really, really easy to forget where one person started and the other ended. He liked it, he was pretty sure. Or maybe he just liked it with Klaus.
"Oh," he said, mouth practically still pressed up against Klaus', his hands reaching for -- he wasn't sure, actually. Just something to touch, any skin would do, same as it was obvious Klaus just wanted to be closer with his knee between Ben's legs. "Well," he said, and decided that he might as well just lean the rest of the way back in for another.