This whole book is about two guys having sex. The twincest part I suspect is there only to make the reader feel like he/she's reading something more "dirty" than usual. It could easily be happening to best straight friends falling for each other and not twin brothers, the way this was written, and the plot wouldn't have changed much.
My point is, even tough this book is labeled as "twincest" it doesn't deal with the subject at all (except with the use of some adjectives that implicate how "naughty" them having sex is, like "unwholesome" and "indiscretion").
If we ignore the twincest stuff (which we can do easily), we are left with almost no plot and two uninspired sex scenes.