Ff, sorry ^^
i don't know if it is one of those ones, but maybe they can get you to the one you want.
http://www.mangago.zone/read-manga/hoshi_yori_hisoka_ni/
http://www.mangago.zone/read-manga/tsuki_to_yabanjin/
http://www.mangago.zone/read-manga/honoo_no_suna/
http://www.mangago.zone/read-manga/futari_no_maharaja/
http://www.mangago.zone/read-manga/senya_ichiya_romanesque/
there's anoher one the prince thinks that the uke was sent to pay the brother debt and be his fiance but i can't remember the name.
Following!!
That's the one, Thanks ^~^
A yaoi where our uke is sold in arabia as a slave gets taken in by the prince as a bride, prince has a younger brother who uke helps care for, we get a hilaious misunderstanding about the grandpa being a lover as he called out to gramps in his sleep