choco strawberry vanilla!! ლ(´ڡ`ლ)
although its pretty popular so maybe you've already read it...
http://www.mangago.me/read-manga/futari_no_musuko_ni_nerawarete_imasu/
http://www.mangago.me/read-manga/kuroko_no_basuke_dj_houkago_dreamer/
http://www.mangago.me/read-manga/kareshi_to_ore_to_ore_no_kouhai/
http://www.mangago.me/read-manga/incest_nekotsuki_izumi/ well it's incest xD and twisted a lot, (i think first ch is about father and son, second about three brothers)
http://www.mangago.me/read-manga/uchi_wa_futago_de_teippai/
http://www.mangago.me/read-manga/pet_keiyaku/
http://www.mangago.me/read-manga/himitsu_no_kuchizuke/
http://www.mangago.me/read-manga/gintama_dj_hanbunko/
What is a really hard yaoi with three or more guys? And a lot of cum maybe?