The whole thing about the MC looking exactly like the brother's sister might be cringy to some but... AT LEAST this is not incest!! The MC can look like the brother's mother or grandmother for all I care.. surely, the brother wont be falling in love with his sister's face but with the heroine's brains and wit..
I do get the cringy aspect, so this is only an opinion..
WHERE IS MY 'THOT BE GONE' SPRAY!!