 If you liked
Futaba-san Chi no Kyoudai
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 ...then you might like
Siscon Oneechan to Kinishinai Imouto
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Both manga's depict the everyday life of siblings who are in this quasi-incestuous relationship. In both cases one sibling is clearly interested in that form of relationship and the others feelings aren't fully established.
Both have sidecasts of more siblings, Though in Futaba-san the sidecast are in a similar situation to the maincast and in Siscon Oneechan the sidecast just builds on more interests in more directions (though the initial younger sister seems uninterested so far in anybody)
Both are quirky romcoms with layers of coincidences, Only main difference is one is shoujo-ai.