I'm going to name my choir "Suavis Cantus" (Sweet Song) and take "Suaviter Cantare" (Sweetly Sing) as our motto. Are they grammatically correct? If they're wrong, do you have any suggestion?
"Suavis Cantus" (Sweet Song) as a choir’s name is correct as well as "Suaviter Cantare" (Sweetly Sing) as a motto.
Anyway, with regard to “Suaviter cantare”, please note that you could also use the verb “canere” and then say “Suaviter canere” since both present infinitives “cantare” and “canere” mean “to produce melodious sounds”.