this looks interesting, could we get a translation?

is that suppoed to be Aoko?

I've never seen more suggestive "fireworks."

lookls like Inui's elder sister

Yes, the hairstyle is Ichiko's. For a moment, I had thought it was Fllay Alster :/
By the way, does anybody know the name of this doujin?

Name is おにいちゃんおうえん隊 by 恋愛漫画家, released at C63 apparently.
Full thing at http://s6.artemisweb.jp/doujing29/tu45/ .