Aki-Sora: Yume no Naka

Both are about brother sister complex with mild nudity  

Two sisters involve their brother in incest relationships 

Yuri love triangle. NTR is more drama, while Aki-Sora is more like borderline hentai 

There is yuri in both. Strawberry Panic has a deeper emotions behind it compared to aki sora but there is seriousness in both. 

deals with brother-sister incest 

Both animes contain lots of H-material. Although there are no scenes of sex in Nisemonogatari, I can't say for sure which one of them is more obscene. But ecchi genre is not the only thing they have in common. Also, there are two sisters in both these titles, one of wich is sporty and another one is hysterical. Moreover, there are bra size 45 class reps, who have a crush on the main character. If you're not the type of a person, who only admires godlike SHAFT style while watching Nise and doesn't pay attention to the content of the show, you'll like Aki-Sora. If you liked Aki-Sora, you'd better watch Nise ASAP, because it's the same thing plus some humour, plot and godlike SHAFT style. read more 

Same premise, boy with a sister complex although there are two sisters who both share an interest in their younger brother; they are unrelated by blood so they don't try and hide their affections. It's more of an ecchi comedy with tons of fan service and the sisters have the Loli effect going for them. Animation is good too ;) 

Sister complex and going beyond the boundaries of morality.