I'm not really sure whether all of them have consent of both families. But I searched out the ones with the best support of the families (sometimes after a bit of "getting used to the idea").
http://www.mangago.me/read-manga/ookami_wo_karu_housoku/ (ukes family knows he's gay, but that ended in a fight. Semes family is total opposite).
http://www.mangago.me/read-manga/cry_for_me/ (in the second stories both mothers are really supportive)
http://www.mangago.me/read-manga/papa_s_assasin_ryuunosuke_wa_tonde_yuku/ (this one doesn't really have a relationship, but the son comes out - unvoluntarily - and father ends up really supportive. Even buys gay porn mags for him feeling really embarressed:D)
http://www.mangago.me/read-manga/netsuai_nante_ariemasen/ (semes family isn't really shown, but uke's family is directly supportive)
http://www.mangago.me/read-manga/tied_up_in_twins/?av=2 (the coming out is a really big deal through-out the story. But just the mother of the uke is supportive, father totally against, but semes father is more like "if it has to be...")
Maybe there is something amongst these that you would like:)
http://www.mangago.me/read-manga/renai_nante_yurushimasen/
This + its sequel + its spin-off
The classic: haru wo daite ita + its sequel
http://www.mangago.me/read-manga/hanayome_wa_juunanasai/
http://www.mangago.me/read-manga/secret_xxx/ is the sequel of XXX allergy ,the seme doesn't have his parents but the ukes family starts supporting him after they see how much the seme cares about the uke
Any BL manga/webtoons where both the families of the seme and uke know about their relationship and they're supportive and happy about it. Thanks