Kimi ga Inakya Dame tte Itte, Toshishita no Otokonoko Recommendations
These mangas are two volumes long.
While Toshishita is more about the main characters, Inakya is about "I like you but you like her so...". But still, the premise is very similar.
The main guys are a year younger, have a bright and straight-foward personality.
The girls have a mother / big sister complex, and treat their interest as children.