Remus and Romulus- oh wait you meant a manga? (just trolling sorry)
http://www.mangago.me/read-manga/land/ (not yaoi, and not shoujo either)
http://www.mangago.me/read-manga/black_lagoon/ (because of "that" arc, not yaoi)
http://www.mangago.me/read-manga/d_gray_man/ (technically it works, not yaoi but defo yaoi material)
http://www.mangago.me/read-manga/gangsta/ (you will cry, not yaoi)
http://www.mangago.me/read-manga/gohou_drug/ and its sequel (it's clamp, so yaoi material, but watch out for the hiatuses)
http://www.mangago.me/read-manga/wolf_guy_ookami_no_monshou/ (look I'm being very litteral here, you said twins and tragedy, both you'll find, but I'm pretty sure you didn't want to read it)
http://www.mangago.me/read-manga/trigun/ and its sequel (definitely not yaoi though it can be shipped, a Classic)
http://www.mangago.me/read-manga/tokyo_babylon/ (shounen ai)
http://www.mangago.me/read-manga/in_autumn_s_last_rain_on_the_right_shoulder/ (oneshot, if you like that one read http://www.mangago.me/read-manga/141108/ next)
OMG! Thank you so much!! I'll read everything!!
Ok. I'm gonna be very specific. I wanna read a tragedy with twins in it. Any suggestions??