"Oniichan to Issho" ("Me and My Brothers" or "Together with my Brothers") by Tokeino Hari 8 volumes-ongoing
Sakura's only family, her grandmother passed away. She is then entrusted to her four brothers that she never met or knew in her entire fourteen years. Very cute story but too bad because I've been waiting for the rest of the manga like forever. It's an unconfirmed reverse harem as we don't know if one of her brothers will be more than just an oniichan. After all, they're not related by blood.