MT is a mezzo soprano, FS has the father role but just isn’t the type for a bass so he’s a bariton. Heinrich and Joseph are both lyrical tenors. Now, the question is: is this opera buffa from the first three quarters of the 18th century, in which case Fritz is sung by a castrato as the heroic primo uomo, spanning the whole range from soprano to alto, or are we talking later Mozart and onwards, in which case he is a heroic tenor.