Who is Rob Vandemeer, Danny Riggs from Smiles to Go and what is their importance?

Rob Vandemeer and Danny Riggs are Mi Su's classmates. Rob plays the leading role in the high school musical, and Danny asks her to the Valentine's Day dance. Neither relationship is particularly deep or lasting, but both relationships, simply because they exist, trigger upset and Will and, subsequently, realizations of how much and how deeply he feels for Mi Su.