Music is, of course, an important part of the Mass. Some parts are sung only by the priest. Other parts are sung by the congregation. And other parts are sung by the Schola Cantorum.
A Schola Cantorum can only consist of males. It is their role to sing the Propers of the Mass, and in doing so, they fulfill a liturgical role and a clerical office, which is why they dress in cassock and surplice. They also sing hymns, and they lead the congregation in singing the Commons and hymns, but in doing so, they are not fulfilling a clerical office.
For singing polyphonic hymns, we also have a mixed choir, consisting of males and females. Their role is not liturgical, as hymns are not part of the Mass, per se, but rather serve to embellish the Mass.
For such a small congregation, we are blessed to have a choir that has a fairly rich repertoire, and we put it in the service of praising God (and edifying the faithful) whenever we can.
One of our many considerations in choosing hymns is the availability of singers. The music the choir sings, polyphony, typically requires 2 sopranos, 2 altos, 2 tenors and 2 basses. And each must know the piece thoroughly well.
It can happen that we plan for the choir to do a certain piece, say, at communion, but we have to change our plans if it turns out that we don’t have all the singers we need. But when everything comes together nicely, you will hear some of the most beautiful music ever written, all for the greater glory of God!