Ore no Otouto ga Konna ni k(ry

The protagonist, Takayoshi, is the eldest of the three Koyama brothers. He has become a fine housekeeper, perhaps because he has been taking care of his younger brothers in place of their often absent parents. The family has a good relationship with the neighboring Nakadachi family, and they have been close since they were children.
One day, the Nakadachi's parents have to go overseas for work for a year, and Takayoshi ends up having to take care of the Nakadachi siblings as well...