Following.
http://www.mangago.me/read-manga/kashikomarimashita_destiny/
http://www.mangago.me/read-manga/kurui_naku_no_wa_boku_no_ban/
But sorry no threesome in it. ╮( ̄▽ ̄)╭
Dounjinshi are self-publish work and it's not only M/M. They are often considered as amateurish and since they are release in small quantities and sells trough web site or convention they are tolerated even if it portrays popular characters, but it can also be original. Sometimes established authors in magazines also write their own doujinshi to give more information or to do fanservice of their series. Hope this help (⌒▽⌒)
1. What does doujinshi mean? If they are written based on popular manga, don't they have trouble with copyright law? I often write stoties or draw cartoons based on the stories or manga I read so I was wondering if they're considered as doujinshi too. Or is doujinshi only related to yaoi? Please explain!
2. Please recommend me some good and completed omegaverse and threesome yaoi.