I did find an answer... a friend sent this to me from the General Instructions for the Roman Missal:
43. For the good of the community and of the whole Church of God, some of the lay faithful according to tradition have rightly and laudably exercised ministries in the celebration of the Sacred Liturgy. It is appropriate that a number of persons distribute among themselves and exercise various ministries or different parts of the same ministry.
The last sentence has a footnote to the GIRM n. 109:
109. If there are several persons present who are able to exercise the same ministry, nothing forbids their distributing among themselves and performing different parts of the same ministry or duty. For example, one deacon may be assigned to take the sung parts, another to serve at the altar; if there are several readings, it is well to distribute them among a number of lectors. The same applies for the other ministries. But it is not at all appropriate that several persons divide a single element of the celebration among themselves, e.g., that the same reading be proclaimed by two lectors, one after the other, except as far as the Passion of the Lord is concerned.
Coupled with tee_eff_em's citation of the GIRM n. 110, it is clear that it is better to have one person per ministry, but that if this ideal/goal is not achievable, then it is allowed to double up
We have plenty of cantors available to sing, so there would be nothing to necessitate the same person being cantor and sponsor. I will bring this up with the pastor, and then re-address it with the sponsor. Thanks very much for your replies! They all are along the same line, and people's preference is to not have the sponsor do more than one thing... Thanks!