Here are the singers, more or less in order of appearance within each clip:

1. Frederica Von Stade, Marilyn Horne, Reri Grist
2. Anne Howells, Barbara Bonney, Kiri Te Kanawa
3. Eleanor Steber, Rise Stevens, Erna Berger
4. Miah Persson, Adrienne Pieczonka, Angelika Kirchschlager
5. Deborah Voigt, Suzanne Mentzer, Lisette Oropesa
6. Malin Hartelius, Nina Stemme, Vesselina Kasarova
7. Teresa Zylis-Gara, Edith Mathis
8. Tatiana Troyanos, Arleen Auger
9. Benno Kusche, Gwyneth Jones, Brigitte Fassbaender, Lucia Popp
10. Sena Jurinac, Hilde Gueden

Just for your amusement, I have put in italics the names that weren’t mentioned, or weren’t mentioned in the right place. All four of them!