Yaois where there's no exclusive seme/uke? Like, they both do the giving and being given i...

Not my cup of tea, but I've searched a link for you: https://www.mangaupdates.com/series.html?category=Reversible+Couple
Enjoy :)

this could be helpful:
https://www.mangaupdates.com/showtopic.php?tid=9820
or this one:
https://www.mangaupdates.com/series.html?category=Reversible%2BCouple&genre=Yaoi&exclude_genre=Doujinshi_Shotacon&perpage=50

Then you want to read http://www.mangago.me/read-manga/when_a_man_loves_a_man/