Kissxsis is really horrible, and the 2 girls are the stupidest "we love our oniichan" generic characters I've ever seen, even for a Japanese manga. Besides the scanlations are made by complete retards.
Mitsudo moe has loli fanservice for example, I don't know about its plot though. Probably school slice of life or some shit.>>>/rs/Mitsudo+Moe
There's also Nuiguru Mix, another school story with ecchi. http://www.mangaupdates.com/series.html?id=18256
But I don't know if any of those are seinen or even slightly interesting.